I'd be lying if I said I didn't enjoy sex on amphetamines. I have had some great experiences with some past partners of mine that were aided by varying degrees of stimulants. But its not a powerful enough experience where I would seek out someone with the sole goal of getting high and having sex. I try to avoid hooking up for a multitude of reasons. However, I know there is a ton of people who DO seek out people strictly to have sex on amphetamines. In the gay community, it is known as Party and Play or 'PnP'. I just ranted a bit about it in a different thread. I was inspired by this thread but after developing my rant I figured I should find a better home.
I gotta echo Spacejunk. When I cum on speed, I seem to skip any relaxing bliss and am ready for more in what seems like a flash. If I do too much, it can impair my ability to get hard. Sometimes if I do JUST the right amount I can get it hard but struggle cumming, which isn't always a bad thing. For me, receptive anal sex is significantly enhanced by speed. This is probably the most pronounced way it impacts sex in my experiences. The second being the enhanced tactile sensitivity/sensations that speed usually gives me.
Honestly, though, having a real connection with my partner enhances sex way more than amphetamines. The psychological component of sex is pretty important to me. Mixing the two together is unforgettable!