Well look what feature I found!..

[5billion]

OK, so you know how Apple offers free single downloads everyweek on the iTunes store, and sometimes the song is crap but you download it anyway? Well, I cleaned some of that up.
I fully deleted all the files and soon after I plugged my iPod in and guess what popped up.. (it went a little something like this..)
"iTunes has discovered that you have deleted some of your perchased music and found it was on your iPod. Would you like to transfer the files from your iPod to your computer?"
I went, "Wow, that's something new."
I believe this feature could only be used for perchased music, but not music that hasn't been perchased (off the iTunes Music Store, obviously).

 

[kornchild2002]

This feature was introduced back whenever iTunes 7 was released. It is relatively old but not many people knew about it. But yeah, it will only work for purchased content.

 

[HAL99]

So....I can delete all the stuff I've bought to make space now? That's freakin' cool!

Thanks man!

 

[pohatu771]

If you delete it, and then choose not to transfer it, it will be gone from both your computer and iPod. It will be gone forever.

 

[bobb-mini]

Now I assume that works only if your PC library is in working order? So if PC suddenly craps out, one wouldn't expect working from a scratch iTunes re-install would automatically bring this little dandy thing up?

 

[5billion]

Yeah, that's correct. You must must must must your iPod synced with that particular Library. It will not work with another computer or iTunes Library. It must be your own.