I've now played through all the story levels and am in the dark matter mode. Using a performance monitor during intensive levels I've seen the CPU run at 100% quite a bit of the time, but so far, so good. Occasionally the display will become a little jerky near the end of a level with high numbers of objects and actions. On a few similar occasions it freezes, but when this happens I've been able to go to Main Menu and use Resume to continue. I don't use the music, and the only sound glitch is once in a while when an enemy tree explodes the sound crackles.
What seems to help is Full Screen mode, which apparently disables the Windows 7 Desktop Windows Manager, giving me some extra CPU.
If it matters to anyone, I've stripped my processes and services down to a minimum, and I've set my Norton Internet Security to go into silent mode during full screen. I wonder if this netbook would handle it as well with everything running.