Welcome to the BBForum. There are a couple of threads that compare the Treo to the BB as many users have switched over.
I myself have had several Treo's (600,650) and ended up with a BB. My main reason for switching was the stability of the BB platform which is way better than the treo. My treo's were constantly freezing on me.
*OS Stability (very simple to navigate)
*Push e-mail RIM is famous for
*Form factor/battery life
*Very good call quality (of course this always falls on the particular carrier)
*MP3/Video playback (included in BB DM software)
*not many third party apps available compared to the Treo
*need a few changes in order for the BB to sync with Mac (in your case)
There used to be calendar syncing issues but with the updated OS firmware, that problem has been resolved.
Overall I'm very happy I switched over to the BB. My Treo's used to constantly freeze on me or crash until I finally got fed up. I was also very surprised on how quickly I was able to navigate the BB's OS. Good luck.