I think I've posted this in a comment before, but here's its own entry b/c I've noticed a number of users taking up one, sometimes two of their five stars for songs that need to be deleted or repaired (stop edits, labels, cd skipping, etc). This is wasteful -- you can do other stuff with those stars!
My rating is zero stars
Play Count is greater than zero
Limit to [whatever] by most recently played
So say on the iPod you hear a problem song ... don't skip but "scrub" to the end of the song (i.e. with the scroll wheel, making sure to up its play count) ... then when you get home those problem songs are right at the top of this SPL.
This SPL also has the side effect of grabbing songs you've heard but neglected to rate. I like it this way, but if you want to avoid it, add another line "Last played is after [today]"