Since the launch of RIM's own-developed app, I've flitted between it and UberTwitter, due to a couple of minor issues. Those problems will be null and void soon, as RIM's update fixes everything I could've wanted done—and more.
If your BlackBerry hasn't received the update yet, you should get it later today. Enclosed in the little update is the ability to edit retweets (rather than just use Twitter's new RT function which recycles the tweet); username auto-complete for saving time after you insert an "@" symbol; and an easier way to search for users, by selecting "go to user" from the menu.
As well as Twitpic, YFrog and TweetPhoto photos are now supported (to view, not to create), and geotagged tweets can be viewed using BlackBerry Maps. Quite a few new hotkeys have been given support, so it's not just "R" for reply—other letters include "L" for reply-all, "F" for retweet, "C" for compose, and "D" for refresh.
Twitter's going to be a bit safer too, as the app can detect when an email address, phone number or PIN code is typed out; warning the user of the dangers of giving out personal information.
I would say to keep your eyes peeled on your Twitter app today—but I know you would be anyway. [BlackBerry]