Seconding [member="Darth Janus"] - this has HIGH potential for abuse.
I like the "but's" you've included (won't stop you from bleeding out from really direct hits, only six minutes underwater, etc.). If we see it being abused, or large groups of people using it as a catch-all for near immortality in battle...yeah, then you'll be super-sorry [member="Jared Ovmar"]! I would also recommend that for future alterations to SmartBlood, that serious weaknesses be included as I only see this getting more iffy in the future.
As long as that's crystal, approved.