I have boxes and boxes of them. I have some stored in photo boxes but the rest fill about 6 shoebox style photo boxes.
One thing I have been doing lately is using Bazzill Lickety Slip pages in between my pages to hold extra pics.I have seen other people do this and it really helps. No reason to have photos in multiple places!
Since my extras started piling up I have been alot more choosy when getting prints. I usually get 1-4 photos from small events and 10-30 photos from larger events. I try to use all the extras in mini books or when I make multiple pages (like if I am making a page of the same event for each of my kids) so I don't have to worry about putting away extra pics.