If you are in the DFW area Sewell and Brian are the people to deal with. There are numerous threads about the excellent service from these people. IMHO Sewell and Lynch are in a class by themselves.
I used my H3 as an everyday driver and never got worse than 15 mpg on the highway and never better than 18 in 44,000 miles of driving. 16.5 mpg is a good target figure.
Kids love Hummers - plain and simple and as a kid hauler they do well. My only problem with the kids was backing up, so I had an aftermarket backup cam installed and I tried to park so I could pull forward all the time. If you go to Utube you will find many kids on offroad jaunts. This one is one of my favorite father and son Hummer videos.
http://www.youtube.com/watch?v=PCp_H4ZTBUk
Reliability wise, the H3 only went back to the dealer twice in two and half years for minor stuff.