No changes you try out aside from those such as Custom Background, Custom Header and Theme Options which are stated on the theme description pages for each theme will be visible to visitors unless you purchase an annually renewable custom design upgrade.
http://en.support.wordpress.com/custom-design/
http://en.support.wordpress.com/custom-design/editing-css/
http://en.support.wordpress.com/custom-design/#custom-fonts
http://en.support.wordpress.com/custom-design/#custom-colors

When using the theme customizer please be sure you are using one of the browsers and versions found here http://browsehappy.com and also be sure you have enabled third party cookies. http://en.support.wordpress.com/third-party-cookies/

NOTE: If you do not have a CSS upgrade then skip using the theme customizer. All of the very same functions can be accessed from your dashboard.
Appearance > Header
Appearance > Background
Appearance > Theme Options (applicable only to some themes)
Settings > Reading (set a static front page)
Site Title and Tagline > Settings > General

I heard that wordpress customizer always have this problem? Seen people posting about this same issue also

Also, if you have another browser installed on your computer, try that to see if the issue is related to just that one browser.

When using the theme customizer please be sure you are using one of the browsers and versions found here http://browsehappy.com and also be sure you have enabled third party cookies. http://en.support.wordpress.com/third-party-cookies/

Where have they split to? Is Stay bugging from the start?

Below, a printed image link to show up the trouble:

http://ebrael.files.wordpress.com/2013/05/personalizar-stay-e28094-wordpress-2013-05-11-11-36-11.png

there appears to be a delay between posting and viewing

Do you mean this happens inside the live previews directly on the WordPress.com site? Please note we did make a new update to the customizer today. Hopefully you will see an improvement.

Apparently wordpress uses coding that should include something specific for the preview to be seen in windows live

Ah, I see. Windows Live Writer is a separate application, and I'm not sure what coding you're referring to. May I ask what makes you say WordPress should include specific coding for a preview to be seen in Windows Live Writer? Did you read that somewhere? If so, a link would be much appreciated. If not, not worries. I will see what I can find out on my own as well.

@fightorflightsurvival, Windows Live? If that is a separate blogging application, then you may need to go to the developers of that program to ask for help. However, you mentioned you're using Firefox? Would you be able to upload a screenshot of the problem showing the entire browser window so I can see what you're seeing?

This shows how to make a screenshot:
http://en.support.wordpress.com/make-a-screenshot/

Live preview is still not working.....can't switch or preview....

New info. There is currently a bug in the customizer preventing it from working for Internet Explorer. We are aware of the issue and working on a fix. It's a core bug, and if you'd like to follow along, you can see the bug report at http://core.trac.wordpress.org/ticket/21707

As a temporary workaround, you can use another browser such as Chrome or Firefox to get around the issue until we can fix the problem.

If you are experiencing trouble and you are not using Internet Explorer, please make sure you are using an updated browser http://browsehappy.com/ then please reply back here with your browser and browser version.

I've had my blog going for nearly two years, love WordPress! But suddenly instead of getting a Preview I get sent to a page that asks for my email address so posts can be sent there. I have Coraline.

That doesn't sound right at all—it doesn't sound like anything WordPress.com would do. What is your blog URL, and is there any chance you can save a screenshot of the full browser window showing where it asks you for your email address and save it to your media library so I can take a look?

http://en.support.wordpress.com/make-a-screenshot/

Im using wordpress from last 4 years, my big and top blog is superb ...

2 weak before.,in 1 day i got 120000+ visitors ..i love to use wordpress.. but there are few things which we really need in wordpress.

they r not something very BIG ,but important for us. so What I was saying...that if wordpress is creating some utility they must give new options.

1) Add profile link option to add google plus profile link.on profile tab. this small requirement but important.

2) remove sitemap limit....my website having 1400+ article..only 1000 is listed in site map.

3) Google added image sitemap option.word press should add image sitemap.either in existing map or create a sitemap for image.

i noticed sometime site map shows images list.,sometime not... this is showing lots of warnings in Google webmasters..

4) atlst give us option to keywords in home page of blog.currently we don;t add tag line.we using tag line,add lots of keywords and this destroys header layout. [I KNOW WORDPRESS DON'T ALLOW FOR SECURITY...BUT WHAT PROBLEM WE WILL GET ] JUST YOU HAVE CHANGE THE TAGLINE AND KEYWORDS...

as your application name is theme Customize r these options will be perfect.

if company plan to remove old style,then you can updated that the way dashboard was changed, to do that a tool was not developed like theme customize.

im sure all users will agree and 4 option ,every BLOG WILL USE ... as far as i feel.

so,pls think...talk with seniors..this is something important and we need it badly...

pls ignore mistakes..

Can Any one tell me what was the use of Customizer option,when all those things customizer allow to do can be done in normal way (via settings tabs) ?

Good question! The main benefit is being able to see the changes live as you make them (a major different compared to the old way). Also, note that old way of changing the appearance settings will probably go away in the future. It's a transition period.

An update on my 9.44am post. It seems there is a conflict going on, the Custom Design colours overrides any settings you try to create via Appearance/Backgrounds.

When you open the customizer, you should see the settings you saved in Appearance → Backgrounds visible and then you can change them from there. I've just double checked this to make sure it's working as it should, so I think if you were having any trouble before it has been sorted out now.

I'm happy to look if you find any other troubles with the Theme Customizer.

@ctpilates, I sent ya a reply by email.

@ccongdn2010, yes, when you re-purchase an expired Custom Design upgrade, the settings should go back to whatever you last saved before the upgrade expired. Looks like you got your domain issue worked out as well.

@theobamacrat, this thread has nothing to do with reblogging and it wasn't having any trouble at the time you posted before. If you still need help, please start a new thread.

The new customization options they've just announced are an improvement on what we used to have. Of course you can see them on your dashboard: they exist now. They didn't before.

As for Custom Design, you can do all kinds of things: what you can do is only limited by your ability to edit CSS.