You know, the only thing I can think of is "pinning" (Which is like a direct Blackberry Text Message). I think it depends on the Mobile5/6 device. I mean the software isn't an issue since with Exchange 2003/2007 you get a superior push vs Blackberry without the need for a extra BES server in the mix. I've been some bad implementations of phones for Mobile 5 and some I would swear by. Same with Blackberry. I've seen some I wouldn't touch with a ten foot pole, and some that are very useful. I find Mobile 5/6 (and even the older Mobile 2003's) are nice I can just add in apps easily and development is pretty open.
I don't know if I can say the development is as nice on the blackberry for sure, but I know you can buy apps for it to. But I think (for example MSN on Blackberry) needs some kind of license to send data through the Rim network.
Not on expert on them, I'll leave it at that but I personally like the Mobile 5/6 over the Blackberry... :)
Well all else fails, make an offering to the computer gods. Preferably in small unmarked bills.