I would avoid taking hard-core science courses like that over a summer. There are two major disadvantages:
1. Your going to have much less time to learn an enormous amount of information.
2. You probably wont be able to cover as much material, so you get short-changed a little.
The only way I would do it would be if it was absolutely necessary as far as scheduling is concerned. For instance, if I was absolutely intent on applying to med school next fall, and the only way I could do it would be to take organic in the summer and the MCAT in the fall--that might be an option.