I was happened to be doing a google keyword search about which sex terms were the most popular, and I was astounded to see the number of searches of individuals looking for clear information about giving and receiving anal sex. It made me wonder if the numbers of North American's putting part A into tightly compacted slot B was on the upthrust? 🙂
According to my friend Cory Silverberg from Come as You Are, in Toronto the numbers are that approximately 25% of heterosexual
adults in the US have engaged in anal sex at least once. And the Anal sex YES site estimates that between 5% and 10% engage in the activity regularly, and cites a survey indicating that 6% of women and 8% of men engage in anal sex at least once a month. These numbers seem to be consistent with the most current stats out of the 2002 National survey of Family Growth suggested that 34 percent of men, and 30 percent of women had tried it ( at least once) in their (or their partner's) rear.
Based on my callers and anecdotal discussions with lots of radio guests I would have guessed about 30% of people use it as a regular part of their bedroom play. I learned everything I tell my listeners about anal sex from a great interview I did in the early 90's with Nina Hartley (during her porn star days. An interview I regularly regret not keeping). She talks of how to avoid hemorrhoids, making sure the receiving party gets a diet rich in fiber, and using a water enema to keep your colon clean before the big plunge. However try finding an enema bag in any modern drug store that isn't medicated and disposable is almost an impossibility. Lastly, she uses lots and lots and extra lots of a good silicone lube as the anus isn't much of a source of fluid. 
Given the numbers of internet browsers looking for more than just the dirty pictures, I'll see if I can troubleshoot an anal beginners checklist for anyone thinking they may want to join the revolution and increase the participation up from 30%.