Oooh in our house the grand clearing-out of under the sofa is a great cause for celebreation! I do it about once a month, and there is always, without fail, a single sock ("Oh! So that's where it went!"), some jigsaw pieces, some unidentified plastic bits of broken toy, at least one of ds's die-cast Thomas trains (cue joyous re-union) and an assortment of rasins, apple peel and hairbands.
The dc bounce around on the sofas while I sift through the treasures (amazing how moving the sofas to a different part of the room suddenly makes them fun ) then we get out all the jigsaws that can suddenly be completed. Aaaah - what more could you ask of a rainy-afternoon activity?