Ooo yea I noticed this a bit back... and is one the reasons I would NEVER want to stop hormones (haha! really, this perk is really entertaining! men really get the short end of the stick when it comes to sex / orgasms... no wonder they have such issues with it).
It started happening month 3 or 4 on estrogen / spiro... and first time it happened I thought I was going to hyperventilate. And yea, the more frequent between playing around... the less strong it is (boo). I'm not really frisky much, but I make it a point to have fun now and then (it is easy to become frisky).
I have also found the nipples being a lot more sensitive. In fact, it has completely changed the way I play around. I start up there and just use my imagination for a while (which, is slower than as a guy, but more fun).
Also, I found I don't look at porn anymore... I "can" and it is nice and everything... but I just don't really need to anymore (I am fine just using my imagination). So this is a complete flip to how it used to be (where i typically looked at things, and rarely just used my imagination).
Oh, andd during I am very very quiet...but physically I try to scoot / get away from it or something (??)... and when it is over become extremely exhausted. Definitely a new / fun experience, haha I would recommend HRT to guys, but I doubt they would really enjoy some of the other effects
Oh, and while we are talking about different reactions, I found that I can find things EXTREMELY funny more often now (and for some reason, when I laugh that hard, I actually start to cry / sniffle... again, uhh...

)
All of this is just another reason that I don't get why people don't enjoy being trans! If we had always reacted this way, we would never be able to appreciate it like we do. Haha I think I might go into too much info when talking with friends / family about the changes sometimes >< I just can't help but share the orgasms thing, it is just so funny / great.