i have a BB 9630; its okay. I thought my curve was a better phone. The 9630 hangs for a few seconds when launching programs or switching between them. I have two 9630's and they both do it. all my family and most of my friends and colleagues use blackberry, and we use the blackberry messenger to communicate. that's a plus.
The BB is pretty quick on the net, but when tethering its not quite as fast. I can get about 500Kbps when tethering; droid in the same location can get about 2.5Mbps. I tried the droid but didn't like it. I prefer the keyboard on the BB; the motorola droid has a keyboard but its just too big. The htc droid is touchscreen only and I will not purchase a touchscreen phone.
Also I'm just used to the BB.
For tethering I recommend a program called 'tether'. I tried different programs; 'tether' is the best.
I would check usage habits before dropping home internet for a wireless card. While the BB internet plan is unlimited, they can still throttle you is your usage is abnormally high. 5GB is the limit on the wireless card; tethering the BB w/ 3rd party software gets you around this but I'm told they'll still look into slowing you down if you cross this threshold on a blackberry.
We use about 30-40GB per month at home (netflix streaming, hulu, WMC internet TV, etc. . )