I've done something crazy that has wiped all 3,000 songs from my iTunes library. They have totally gone from my iMac hard drive as well.
Fortunately I have DVD back-ups for about 2,600 songs.
I know there is a way of syncing from the iPod (where they all still exist) back onto the iMac, but I can't remember how. I think there is software available for it. I'm hoping some of the computer wizes on here can help...

No experience personally. About the only thing I can say is that you appear not to be alone. If you type 'itunes songs disappeared' into a search engine, quite a few entries come up about the problem. Some are people saying 'me too' but other entries have information on what may have happened and tips that may help to get the songs back. I'd suggest a read of the first few search result pages.

Sorry I can't help with the problem other than that.

I think you need a third party app to get your music off your iPod to your Mac.

I use a PC and there are dozens of such applications but I am not too knowledgeable on Mac applications that do such a thing.

Doing a quick Google search, I found this:

http://www.crispsofties.com/iPod.iTunes.html

Give it a try!

Sorted.

As I may have mentioned elsewhere on this board I downloaded Music Rescue from the Apple Store and copied all the songs from my iPod back to the computer. I then dragged them all from the hard drive to a new iTunes library.

It was a slow process that maybe could have been quicker if I'd read the instructions. (I'm an Aries: We Arians don't do instructions)

I commend this download, which costs £10 in the UK but I'm sure is equally affordable from the US store.