Twice isn't very strange, I don't think. There's usually a few seconds to a minute of not-super-fun-fuckin' after that first nut but once I'm through that it's all systems go again. Thrice, not so much, at least not without even a short break.
Being stoned is great, and I find having had a drink or three often makes things more fun as well. Also mammoth sessions of multiple goes are awesome, with a minute or two and quick sip of beer or something in between. By the end you're all sore and shooting blanks but it's fun and the sleep after is excellent.