per a FR thread, this was 'documented', after i think a denial by SULLIVAN that he was seeking a partner for "BAREBACKING"(take a guess what this means!!).
Sullivan did post ads on two such sites, but nobody ever proved he was ever looking for anything more than regular dates. (Supposedly, a lot of non-"barebacking" gay men prefer those personals sites because they're far more hidden in the background ... in other words, your family and friends won't find your ad seeking other men like they might on Yahoo Personals.) For Alterman to refer to it as he did is disingenuous at best; he's simply trying to smear Sullivan with as much mud as possible.
But then, there's a reason Alterman is considered one of the most hated people in the national news media by other journalists.