When is it time to get up?

[DeadManJay]

This question might seem ridiculous, but I'd like to know the popular opinion. Do you guys set a nightly goal? Is there ever an amount that when you hit it, it's time to go home and get some sleep?

The reason I ask is that I had one of my best runs of cards since I've been playing NL in the casino the other night, I was up about 6 buyins in 4 hrs. I don't think I would have been in such a hurry to go but there was still someone (that I respect) sitting at the table that had me covered. Was I dumb to get up and leave from a table that was capable of producing this kind of money or smart to get out while I was ahead?