Well that was fast… I lasted 49 minutes and finished in 1,687th place out of 2,247 players.
I was doing quite well for a while. I alternated being table chip-leader with another player a few times. I picked up several small (< $300) hands and lost a couple of small hands. Then I hit pocket Kings and felt like I could bet. I bet and only one other player stayed in. She bet something like $2,200, and I called. The only thing she could have had to beat me was pocket Aces… and that's exactly what she had. I should have realized that and folded, but I didn't. There were precious few showdowns at the table up to that point, so not a whole lot of data to go on. Oh well. It was fun, and I'll be entering more tournaments. This was a learning experience.
Joey Gibson's Blog 
Bad luck, Joey. You only face Pocket Aces about 1 in 44 times at a full table.
Some advice I picked up from Phil Gordon occasionally helps:
The 4th re-raise means aces!
If I can, I try to arrange the betting to see if my opponent will make the 4th re-raise while I still have enough chips to lay down my kings.
For example, if the blinds are 50/100 and my stack size is 3000 i would make my normal raise to 300. If my opponend raised to 900 (the standard re-raise amount), I would raise by 600, leaving me 1200 chips. If my opponent raised me all in after that, I would strongly suspect aces, and might lay down my hand.
Practically speaking, however, opponents in online play are more aggressive than live play. They may act like this with as little as AK or TT, so your call was reasonable.
Thanks for the tip! I’ll keep it in mind next time I play.