Sure, keep a laptop on. I've kept a laptop on for months. It might help to elevate it (by placing it on some CD cases for example) so that it can get good air circulation.
Remember to go into the Power control panel, and make sure it isn't set to go to sleep or standby after [x] minutes/hours.
Otherwise, assuming good air circulation, you should be alright!
- rp
(your avatar gave me a few seizures while writing this post)