* The new interface is faster when running, but it's slower to launch.
* The new interface requires time-consuming mode switches. Specifically, in the old version I'm in my browser and I get to stay in my browser to do other things. In the new version I have to run a Java applet, kill it, start my browser, and only then navigate to a site of interest. That's a pain, reminiscent of the dark days of running binary software on Wintel PCs.
* There are some goddawful strange interface quirks, like non-smart editing (quotes don't get inserted the way they should), and you have to pull up the whole frickin address book any time you want to send an email.
* There is no one-key way to quit the app.
* It asks me if I want to stay connected so it can get data, but then a) it asks me again (and again), and b) it still doesn't check my mail.
* Sometimes on sending emails it locks up so badly that I have to pull the battery from my phone and reboot.
So, when do I use it? Now and then when I'm in a crowd of Blackberry users on a transit train, plane, etc. The new interface looks very nice, even if it doesn't work properly.