I suppose I should start at the beginning. My somewhat-odd work schedule makes it very easy to travel in the summer. Thus, I have a good window to work with. Although there really isn't a "low season" for Las Vegas, the summer is a bit slower than other times. Airfares are still way too high (this year, anyway) but doable, and reduced room rates are a wee bit easier to score, especially if you are able to get a comp.
So this time I'm going in early July, actually the week of July 4th, which is a bonus. July 4th is a Wednesday this year, so it will be a bit less crazy than a long weekend.
Yes, Vegas in the summer is hot, too hot for some. It's a dry heat, so it's much more comfortable than a hot day here in Boston, but anyone who tells you "you won't feel it" is full of crap. When it's a hundred and six degrees, you feel it. It is too hot, for me at least, to play golf or hike the desert, but I can walk around outside or sit by the pool and be alright so long as I stay hydrated. I also do the siesta thing when I need to. It's hot, but not too hot for me.
Next up - picking a flight.