I think the "fitter people sweat more" thing makes sense too...I'm another small woman who sweats quite a bit, and my sisters who are slightly thinner than I am always give me a hard time when we run together about how sweaty I get compared to them. They don't do as much running etc. as I do. In addition to sweating a lot when it's hot, I also have a lot of vasodilation (read: I turn bright red!)...but I still find the heat really uncomfortable to run in and do much better when it's cool out. I don't know how those of you who live in southern climates do it!!

As for the mosquito thing, I do find that being "sweaty and full of hot air" attracts them--on buggy trail runs, I'm OK as long as I'm running but if I stop for any reason the bugs immediately find me and are a royal pain!