Paris in August has a rather different feel. The Parisians head to the south for the beaches leaving the tourist to rule the city.
A lot of the private shops, restaurants and cafés are closed ( even my favourite one... ), so one needs to look around if you wish to dine a bit further from the main tourist attractions.
Still there is so much to enjoy :) . The days can get hot...but its not an issue to me. I enjoyed sitting at the Jardin du Luxembourg and sipping my afternoon coffee :) Oh, I had such a great time.