Kristoffer Winters, a 31-year-old New Jersey native and an actor (he had a small part in The Hurt Locker) in his own right, is definitely Jeremy Renner's partner; it's just a matter of figuring out whether they're partners in love, business or both. According to a January 30, 2010, piece in the L.A. Times, the guys had owned a Hollywood Hills home together since 2008 that they refurbished and were recently able to sell for over twice what they paid (nice in this market!).
The comments on Perez Hilton over this are overwhelmingly defensive toward Renner's privacy, though I don't think the same people spend much time bitching about the privacy of every straight star on the planet, even the ones who have told people in no uncertain terms that they are not interested in talking about their love lives (a dwindling number, to be sure). I think it's mostly from people who believe they're protecting gay people (wouldn't it be more effective to lobby the producers who are supposed to be discriminating?), partly from people who think they're protecting gay people but also secretly feel like being gay is an icky secret and, in this case, partly from people who despise Perez Hilton.
I don't see the big deal in discussing this; Renner's an adult and from his interviews seems very cool about gay rumors (even kind helping to start them about himself). If he's not gay, that's gay's loss.