PocketInformant is the a PIM application that had a very strong following on the Windows Mobile platform. Pretty much the must have PIM. Obviously the BlackBerry version will not have the feature set matching the WM version, but should give those of us lacking a decent PIM a good option.
As a previous PI user on a WM5 device I was excited to see PI for BB. I tried the private beta and was disappointed with the sync'ing option. You had to basically sync the BB with your Outlook and then sync PI with the BB Calendar. Lot of monkey business IMO. I'll have to head over and see if they changed this to make it more convenient.
The comments on the product page are a sort of get out of jail free card as I'm sure Alex doesn't want to waste time tracking down bugs on beta OSs with issues.
I'm using the trial with 4.5.0.69. The trial is a little limited on the data you can use, which make it hard to truly trial, but overall the latest beta looks really pretty good. I don't seem to get any tasks to sync. Not sure if that is one of the 4.5 OS issues. Might have to try a different OS and see.