I have a the WiFi iPad 2 and I do regret only getting the WiFi version. With the original iPad, I bought the 3G version and barely used it. I think I used 3G two months of the 11 I owned it. And when I switched to the Verizon iPhone, I got a tethering plan, so no need to pay for a 3G data plan when I can tether.
But that's where I was wrong. I didn't use 3G much on my original iPad, but I DID use it. Now I have to pay $20/month on my Verizon bill, that sometimes goes unused, and I can only get Verizon 3G. I should have purchased an AT&T (or GSM) iPad 2, as I learned in May while on vacation, I was in a Verizon dead zone, but AT&T had perfect coverage (my brother has AT&T, and was getting 4+mbps). This way, if Verizon doesn't work in the area I'm in, I have the AT&T option, and vice-versa. So I actually plan on selling my WiFi only iPad and splurging on the 3G version of the iPad 2. I removed my tethering plan last month, as I really wasn't using it. But my workplace doesn't offer WiFi, and I work alone on weekends, so I like to put Hulu or Netflix on in the background from time to time while working.