If you mean the quick post thingy at the top of the window, that's not the main post editor, the usual one is still there - just hover your cursor over your display name at the top right part of your grey admin bar and you'll see a drop down list and fly out menus with the name/names of your blog/s. Put your cursor over the name of the blog you want to post to, and you'll see 'New Post'. That's the one to use.
You can also access the same via Your Dashboard - hover your cursor over the name of your blog and you'll see a similar dropdown/fly out menu - choose 'new' - then 'post'.
The preview button is still there, so are the modules for tags, categories, etc. If, in that screen you can't see the modules you want, look at the top of your post editor window and click on 'screen options' and choose the ones you want from there. You can also move modules about to suit yourself.
If this hasn't answered your question, and you're having problems with posting in some other way, then maybe it's a bug. In which case you may have to contact staff. We're just volunteers here, currently.