I agree with everyone else here. I've only had the 8830 for 4 days but really like it. I'm a long time Treo user (lately 700p). I had become very reliant on email and while Versamail worked fine, I really wanted more.
I am also with Sprint and had to add the Blackberry Data Service to my plan. They say that I would have to pay more in order to be able to use my phone as a modem but I'm not sure if that is exactly the case. I'll try that this week.
The only thing that I am disappointed about is the lack of the ability to edit office documents. Since the Treo comes with Documents2Go, I used that very frequently. I've got documents and lists that I carried with me and made changes to all the time. Now it looks like I'll have to buy something. Docs2Go says they will be coming out with something for Blackberry soon though.
Applications for 8830 are a bit scarce though. I am also still looking to replace a few other applications that used on the Treo and it looks like there aren't any free alternatives so I'm trying to find some low cost alternatives.
I hope this helps.