After two weeks of riding in 90+ temperatures, it's definitely getting easier for me. Becoming acclimated to the heat and humidity is the key, and commuting is a great way to do it because you have a relatively cool (altho humid) ride in the morning and heat in the afternoon. Yesterday I rode a century with temperatures near 90 F the last couple of hours, and it didn't feel too bad at all. However, if I hadn't been commuting nearly every day in the heat, I would have suffered.