It's not my primary connection for the iPad ... I use the AT&T plan, but it usually connects when AT&T won't, and it comes in really handy as a good way to get around the 20M limit for application download.
I use my Droid to tether my iPad every day. It does not require that your iPad be jailbroken but does require that your android phone be rooted. The app on the android market place is called wireless tether for root users and I think it is free. Android 2.2 will include Tethering but nobody knows if the carriers will allow it with out additional cost. The good news is that Verizon does not charge extra for wifi tethering on the palm pixie. It was for this reason that I have not purchased a mifi and did not buy the 3g iPad.