I didn't know that Google music allowed you to store 20,000 songs - Seriously thank you! My current collection stands at a little over 12,000 (including a huge amount of FLAC from all the CD's and vinyl records of mine that I've ripped over the years) so this is backup for the whole enchilada.
I only wish this was here back in '06 when my external drive fell off my desk and I lost my music (didn't have money for extra drives back then and hadn't backed up all my music to DVD). I lost a bunch of Dennis Miller monologues from the last few months his show was on there air - funny stuff.
I had been ignoring cloud everything for a while because I like to wait until things settle down rather than jump right in. Now that I've been looking into it - with pointers from people like yourself - I'm impressed with what is available for free at this point in time. My music collection is 136GB because of all the FLAC audio I have, so it is quite a relief to have an off site backup for such a large amount of data. This will also free up some space on the microsd card that I use with my Transformer, since I can access my music from google instead of deciding what songs to have on the card.