I always saved my single tracks in wav format.
When I downsize a picture I even keep the original. Fills my HDDs but I'll have until the day the drives crash

Wav or aif but mate I beg to differ on the mp3 format ..well now days any way  radio here in Oz eg triple j unearthed which is sort off broadway arm in the national broadcaster plays mp3 ...preferred format in fact. Also synch placements particularly for bg music TV isn't all that fussy either as long as it sounds good. So don't beat ureself up
greg
   

Your original file stored locally on your hard drive will not deteriorate ..... sending it off to people and sites on the internet will also not deteriorate it ... but if you upload it to a site and then downloading it again from that site you probably will hear a difference as sites do tend to re-sample MP3s to make them smaller.
This is my experience with it anyway.

But you are right though ALWAYS keep an original in WAV or other good quality format.

You should also have a back-up drive. A few members have had experience of their main drive. 

Thumb drives, they are cheap, easy to back up to, and a physical back up that won't eventually fail like a hard drive.  Yes back up moth wave and mp3,, I do this from I tunes, but I also back up all my recording project files, to back up drives and thumb drives.  Thumb drives are labeled and filed, smaller and easier to keep than CD's or DVD's.

thats an excellent tip man I am seriously going to start doing that!!!