I too just picked up a '77 XS400. Mine is in okay shape considering it's been sitting in a garage for 12 years (price was right = free!). I know I have some work to do, but she was running when she was parked, so it gives me a little hope.
I'm also interested in anything noteworthy on this bike (recalls, electrical gremlins, etc.)
If she doesn't have any major issues, I plan on modifying her to a cafe style, so if anyone has any hints, tips or tricks that may help with that direction, I'd be interested in those as well (I'll be searching the forum in the meantime...)