I have 2 gb and I've set mine to 1000 mb. Been running like that for a month now with no problems. Before deciding I ran Pagefile Usage Monitor for a while and ran my computer under heavy load. The pagefile never went over about 600 mb.
I read in the engineering blog that the Windows 7 rc default PF size is automatically set at 100% of system ram. It's working fine for me. My machine has never been faster or more stable. I see no reason to change anything.