AC adapter popped.
http://docs.info.apple.com/article.html?artnum=302461
Unfortunately the article does not explain what to do if the ac adapter overheats and pops, or if that is covered under my warranty.
Thankfully the battery was full, so I was able to back up all my data.
I'm going to take my laptop in to the apple store tommorow.
MBP 15 inch, Pb 12 inch, imac Mac OS X (10.4.9) Bootcamp on mbp 🙂