I've had my V4S for about a month now, using it as a commuter.
I'm in Socal, and it's been 75-85 degrees F riding home in the afternoon/evening. We can legally lane split here, which helps. Stopped at a light, if I put my feet down, the heat is noticeable, but not "scalding" or "burning" or some of the other adjectives I've seen used here on this forum. I'm usually wearing regular blue jeans, or sometimes gym/athletic track pants with gym shorts underneath.
I agree with orman above that the seat itself is not the issue - it gets warm, but never HOT. The hottest parts of the bike - I borrowed a thermal imager to confirm this, I should have saved the picture - are:
(1) the frame covers - the silver blades in the middle of the fairing, running underneath and parallel to the fuel tank
(2) the subframe covers - the black plastic lightning-bolt-shaped bits, directly aft of the frame covers, that contact your inner upper thighs
(3) the leftside head cover - the black plastic shroud that says "Desmosedici Stradale".
I'm still going to try the heat shield mod on the seat described by torrific, since I'm enjoying tinkering with the bike thus far. I've already replaced the useless stock mirrors with the aluminum set from Moto-science, and they do a pretty good job, taking care of another one of the bike's stock weaknesses.
At the end of the day, this is the most mind-bending, soul-twisting, universe-warping bike I've ever owned, and some heat isn't going to stop me enjoying it.