The cabin heat can be uncomfortable on a warm day with the top down. It doesn't bother me too much, but I tolerate heat very well (I used to jog in 120+ degree weather when I was in Kuwait).
On a hot day, stopped in traffic, with a slight breeze blowing perpendicular, you sometimes feel like your being slowly parboiled. You can't wait for the traffic to start moving again! Of course the best cure for that is to open it up on the freeway and try for a good wind chill effect.
The side sills can leave burn marks on your legs if you are wearing shorts and aren't careful about getting in or out. With a little practice and a burn or two, you learn real quick.
You need to ALWAYS remind passengers (particularly ladies in shorts or skirts). They don't like it when their ***** hose melts.
BTW It is a lot of fun helping a nice-looking lady out of a Viper when she is wearing a really short skirt.