Don't most people, really, use iPads over wifi? Or am I just one of the cheapskates who bought one without 3G or 4G support?
I bought an iPad 2 last year and I didn't even consider buying one with a data plan. I am near wifi about 99% of the time, discounting driving, hiking, and airplane time. In a pinch, I can check email on my Droid.
Eventually 4G will become inexpensive, but it isn't right now.
I rely on the 'always on' internet connection that 3G provides me. When I need to look something up, I don't even think about wifi. I just look it up. There is value in that.
No. I don't use the work wifi because it is severely limited (paranoid IT guy) and my iPad may access material I'd rather they not sniff (just NOYB stuff). I use it on the road for mapping, impromptu parking-lot Grouponing, whatever far from wifi. Open routers still often have some irritant signin or blacklists. Even at home my iPad often gets 3G better than wifi.
Don't underestimate the value of "always connected". A legacy unlimited plan multiplies it.
I sometimes trust 3G (and now 4G) more than I trust the available wifi, even over a VPN. Admittedly it's not that hard to put up a fake base station, but it's basically unlikely. Sometimes wifi at events is just badly run or overloaded, too.
There are also sites with rules about what's allowed to be on the network or not. Often a consultant or guest can't put his device on the network, at least without a lot of work (BYOD isn't done on many networks), but having network access is useful. There are also sometimes IP considerations (using an iPad or 4G hotspot during a break from a day job is less likely to be "using employer resources" to manage your startup if you're moonlighting than if you use their wifi...).
For +$130, it's worth it to me to have the capability. It also makes GPS more accurate, and maps is a really cool thing. I only replace my iPad every second generation, though.
I used to know someone who worked at a facility where he didn't trust the wifi (perhaps he thought they were running bluecoat or something). He just used an iPad 3G for all his personal stuff. He was pretty well regarded, so no issues on productivity/etc.
Still, I bought a 3G ipad only because of the GPS chip in it. Even without the data plan it's quite valuable if you hook your ipad to your phone's hotspot or another wi-fi network.
I bought an iPad 2 last year and I didn't even consider buying one with a data plan. I am near wifi about 99% of the time, discounting driving, hiking, and airplane time. In a pinch, I can check email on my Droid.
Eventually 4G will become inexpensive, but it isn't right now.