Damn it, finding ubuntu to be kind of... crashy. After a day of light/medium use it gets slower & slower until I just have to smother it w/a pillow (by which I mean hold down the power button).
No clue how to diagnose the problem.
@FreedomATX yeah, thanks--I was not familiar w/that. Looks like there's an included gui System Monitor app too. I'll keep that running & see if any culprits become obvious.
@rpardee Huh. Maybe use top to see if anything stands out for CPU/Memory/whatever?