I've been running a version of some sort for 6+ months now. It stinks. Then again, so does the IMAP interface, though slightly less.

I cannot file/tag a message in the BB app. I cannot select text in the BB app. I cannot highlight and dial a phone number from the email body in the BB app. I cannot display URLs in the BB app. New mail arriving in the BB app doesn't trigger the notification on the device.

There are lots of problems with the BB app version for hosted apps.

It isn't push; it polls, but the polling interval is pretty short in my experience.