Hi,
Some feedback with cloud rendering.
first, huge thanks to Awong from sidedFx who help me to send succesfully my job in the amazon cloud.
At the same time, I try to render my scene with Gridmarkets and it was really a great experience. It's really fast, faster than amazon ec2. I render 3056 HD frames in 4 hours. it's simple and efficient. Probably cheaper than EC2 (i have to wait the bill from amazon to compare).
So thanks to the gridmarket team too. Keep going !

it would be nice if you put your bill and frames rendering time comparison here.

I can also report on Gridmarkets and must say its absolutely amazing. I am very impressed with their service and speed.