In my opinion these are the top features missing in wordpress.com:
1) FEEDBURNER INTEGRATION:
Being able to redirect all existing subscribers from http://yourblog/feed to your feedburner address. And making that feedburner address be the autodiscovery address for new subscribers.
Today you cannot know how many subscribers you have.
* That can be configured to include the social sharing services you are interested in (in my case some international and some Spanish: bitacoras.com, delicious.com, fresqui.com, friendfeed.com, facebook.com and meneame.net)
* And that can be automatically added at the end of each post
What do you think? I wish wordpress.com had a list like Dell's ideastorm where we could vote for feature requests (and see which the most popular are.