I'll admit, this has been the toughest thing to deal with. At the moment we've left a sort of breadcrumb trail with family members in various parts of the world (a box here, a box there, almost exclusively with photos). I like the idea of scanning everything, but for those of us born well before digital cameras became the norm, that would be a lot of photos. :-)
Scan and put them on dropbox/flickr? Use iPad or one of those digital frames to display them?
Do you really even look at them? When I'm with relatives, I remember events, not pictures. I say dump the photos.