http://savingtosuitorsclub.net/showthread.php?145-Exactly-what-does-the-IRS-agent-think
http://losthorizons.com/CtCforFree.pdf
Of course, have 100 bitcoins in your account is meaningless, but the moment you sell those 100 bitcoins for $800 you have to report that. Having bitcoins is like having 100 jpgs or 100 bookmarks, you don't report jpgs on your taxes even though they may have value, but if you sell them then you report that, same thing.
The great thing is you only need to report it once the dollars become "real". No need to report mtGox dollars or Dwolla dollars. Only once it hits your bank account. I would just seriously hope dwolla doesn't get shut down.