not quite a full-fledged hack but i liked richard's idea of sanding down the mackis drawers to fit the expedit bookcase. a great idea if you're thinking of ways to organise your bookcase.
"the drawers are stock ikea drawers, but i had to sand quite a bit (3/16", i think) off the boxes to make them fit. it's really annoying that they don't just naturally fit in there, but with them stuffed into the shelving unit it has a bit more structural integrity now. i also added a wine rack out of some plywood left over from building a pair of donald judd-style benches." link.