Messages Inbox - you can select which email accounts, and mms/sms are displayed within the inbox. The sms/mms & email separation isn't a new thing, but now you can actually select which email accounts are displayed within the inbox. Great if you have work and personal email accounts on your device.
Other than that, now you have an option at the main menu for display changes, etc... wallpaper changing, and of course the ability to change some native BlackBerry theme formats. Zen and Today are one thing.
There are a lot of other minor changes here and there as well.
The Browser will apparently get tabbed browsing at one point, too, one of the leaks had, it but had been removed since then.