I have camped a LOT of things.
In Cata, I camped the rare spirit beasts. Longest camp for one was the bear in Northrend. Spent about 16 hour straight waiting for it.
I used to camp TLPD, until I logged in three times after taking a break to find him dead underneath where I logged out. Since then, and cross-realm, haven't bothered.
I got 6/7 of the WoD mounts. Most I didn't camp for long and were just sheer luck being in the right place at the right time.
I camped Poundfist on and off for 2 days using a second account while I played my main. The second night I went to bed at 12pm, since it was 2 hours past his supposed max-spawn and I thought he might spawn the next day.
Unfortunate for those that had camped a full 3 days there, he died at 4am server time, without anyone knowing, because two guys questing thought he was a normal rare. We only knew after one of the guys linked a SS on our forums. A lot of people were pissed.
Pretty sure I've given up on Poundfist for now. At least until they possibly change the way he works or something.