Today begins registration for the new .xxx domain names. I found an excellent article in the International Business Times that explains the registrations schedule far better than I could and it includes a chart: .XXX Domain Registration: A Cheat Sheet for the Sunrise
I do not care for the segregation aspect of .xxx and feel that it will make blocking all adult websites, no matter how conservative in design, much easier for ISPs, hotels, and anyone else that so desires. However, if you already have a TLD (top level domain), you really do need to buy the matching .xxx if nothing else.