I delete them at the end of the month but before I do so I scan them all to
1) like Kathy feel 'proud' that although I felt like I wasn't getting much done that I actually DID achieve a lot
2) also like Kathy, occasionally some vital piece of information slips through the cracks - someone's cell phone number that didn't get entered from a new business contact etc - the name of someone in a store that I didn't note in my contacts but is on a completed to do....etc...

Just occasionally I've been glad they're there.....

cheers
Helen