We Love Free Porn and
Had A Few are similar sites in theme and both index pages include the "free porn" phrase, so Google will surely make the connection.
One specific benefit will be that, in Google's dbase, the phrase "free porn" will be more associated with both sites as a result.
If for example a PR5 page about "phone sex" placed an unrelated link to "speed boats", Google would not place as much trust in that link as it would have done from a PR5 about "boats".