The open source drivers on cause my system to overheat quite badly. Now that 10.04 has the fglrx drivers I've tested and confirmed that the issue is related to the open source drivers. Basically, with fglrx drivers my system runs at around 35c - 40c, but with the open source drivers the coolest it gets is 50c but it often goes even higher.
Does anyone have any information about this? A Google search didn't really return any helpful results.
Edit: my GPU is Mobility Radeon HD 3650