I just noticed that about a quarter of checked songs in my iTunes library are no longer on my iPod mini 4GB (updating is set to automatic) and 'update songs' doesn't copy them back (also not after unchecking, updating, rechecking, updating again).
There is enough space left on my iPod for the selected songs to be copied.
Solutions on Apple's website don't solve anything (installing latest versions of iPod updater and iTunes).
In my dispair I decided to see if playing some songs in iTunes would change this, and it did.
Nice! The songs copied to my iPod and I can now play them again.. but..

playing every checked song in my library is going to take more then two days, so I was hoping somebody has a faster sollution.
I'm considering trying to import everything again, but I don't want to make matters worse - I have a 'solution' that seems to work, and coming from using windows, stuff like that seems to have the tendency to create more problems. I would also like to keep my ratings and play counts if possible (don't know what importing again would do).
Thanks.