Actually, I'll beg to differ on this, DC. The first time we went to Paris was in August, and it was great in that it was less crowded than it usually is...not that it's the kind of city that usually feels overcrowded. More than enough restaurants and cafes open, Parisians around and things to do. The overall feel of the place was as though everyday was Sunday, which was actually quite pleasant.

Now, in August one runs the risk of a heat wave, but that applies to most of Europe in August. And even the couple of very hot days we experienced were not overly oppressive. The only advice I'd give on that score is to read reviews to ascertain whether a given hotel's air conditioning is sufficiently strong to deal with a heat wave.