People (mostly virgins and idiots) say there is no such thing as bad sex or bad pizza. More accurate is to say that average sex and average pizza are both satisfying, especially when you're in Italy.
Perhaps inspired by this idea, Chicago artist Jason Salavon found the average look of Playboy Centerfolds for the 1960s, 70s, 80s, and 90s by digitally averaging the images. The result, Every Playboy Centerfold, The Decades (normalized), from 2002, is below. It's a cool idea, and the results are beautiful, but apart from the gradual slimming of the body and the use of brighter lighting over the decades, there is not much to conclude other than that, on average, centerfolds have great posture.
The 1960s--->70s--->80s--->90s
Perhaps more relevant is Salavon's 2001 piece 76 Blowjobs, his averaging of 76 "found" fellatio photos. It's a great representation of how even though you may never forget your first time, by the 76th, it all becomes a blur. Plus, of course, that an average BJ is better than no BJ at all.