I've not seen any lag at all myself, then again I have recently upgraded my computer.
Yeah, I'm using a $300 laptop I got from walmart about 4 years ago. But it has a 2.14 ghz processor and 4 gigs of ram, so it should be able to handle such simple graphics. It seems like it has something to do with the backgrounds, because my game is fastest when in the ship away from the cockpit, and slowest when on a planet. I can see my game noticably slow down when I enter the cockpit and it starts showing the background planet outside.