It's defnitely legal in the U.S., but as far as I know it's up to the individual
to keep track of the cost basis, and that can be a mongoloid pain in the
ass.  But there's no law preventing the spending of bitcoin or altcoins that
I know of, and I'm pretty sure I would have read about it on bitcointalk
if there was.

If you can load funds onto a card, that would be awesome.  Finding a place
that accepts altcoins is no easy task tho.  Can't say I've ever tried.