Depending on the technology, there are many things to consider before jumping into bed with a WISP. I get my service from an ISP with a wireless division, though it's not their core business. From my understanding, the technology used is a mix of 900Mhz and 2.4Ghz, depending on distance & line of site. The closer and clearer the LoS, the more likely they will put up a 2.4Ghz antenna. Otherwise, it's 900Mhz. Often it requires mounting on an antenna tower, unless it's cellular based.
Problems I've had with it are mostly related to bandwidth saturation. Quite often these wireless PoPs will be piggybacking on one another to a central location, so unless it's properly provisioned, be prepared to be frustrated. Also, many times the WISP will put their tower on a pre-existing structure and depending on security situations, they may not be allowed to go on-site unless the owners of the property are also on-site. Think places like central grain storage co-ops and the like.
My connection is a pretty poor value. I pay roughly CDN$70 for a connection that is, at most, 1Mbit. The upside is that it is synchro, so while my downstream is pretty low, my upstream is better than most. Ping times are all over the place, but that is more a function of an over-subscribed service than anything else.
Cellular based technologies are available here, but the caps are dangerously low with overages being charged at a pretty obscene rate. And it doesn't work with my pre-existing router, which is a big negative for me. Rogers Wireless is I think $25 a month, but that's for only 500MB if memory serves. I can't verify this at present since the Rogers website sucks hairy arse.