It's something I've learned to control over the years... naturally I haven't been so good at controlling myself at the beginning of my "career", but it's very much under my control now...
In most cases, my girlfriend has an orgasm within a reasonable amount of time - say 15 to 20 minutes (though sometimes less, but sometimes not at all during penetration), so I'm not under a lot of pressure to "perform"... what is more important to me is for us to have an orgasm at the same time, which I'm constantly improving on, and is a great satisfaction...
On several occasions, I've also been able to ejaculate, change condoms and continue without losing erection...
However, I have "over-controlled" myself on more than one occasion, which resulted in no orgasm for me, not matter how long I tried...
EDIT: oh yes, I'm also uncut...