Houston can be a challenge to ride in -- I should know, since I've lived in and around Houston for all of my 37 years. The problem isn't so much the people as it is the fact that Houston represents the kind of spread-out sprawl you get when a metro area has no zoning and no planning to speak of, and everything seems like it's a long way from everything else. Here, the car (or truck) is king and the needs of cyclists are really not given much priority.
Having said that, cycling around here is not a lost cause provided you are willing to travel a bit to your starting point, or if you live out in the suburbs and are close to some of the outlying farm-to-market roads. If you get out a bit to places like Magnolia, Montgomery, Conroe, Willis, Fulshear, Sealy, Coldspring and so forth you'll find some sweet roads to ride on and some nice trails for MTB action. As for riding in the inner-city areas, well, that's only advisable if you have a death wish.
As for the heat, if you keep hydrated and keep moving you'll do fine. It's no worse to deal with than the sub-zero torture that passes for weather in the northern climes -- tonight I went riding in 68 degree weather; how about y'all?
