They fit, are comfortable, and don't shred in the wash.  The only down side is that the are a lot warmer than briefs and lighter boxers.  They're great in the winter but during the summer they are sometimes one too many layer of too much cotton.

One problem though - they don't play well with tight jeans.  The skivvie legs roll up when you pull the jeans on and you end up trying to tuck them back down again.