Well, technology is here to help in that very, very specific situation. There's an app called Bed Beats that's been around for a little while, but it's just starting to get a lot of attention now. Here's how it works: You fire up the app and put your phone on the bed when you start having sex. Then it detects the vibrations on the mattress to figure out your speed, and it plays a song that matches.
If you're interested, it's available for iPhone and Android and costs $2.79.