Not a fan, but I commend him for his guitar playing. He's awesome. Too bad it doesn't shine through on his album, I had to find out in a live performance by Maroon 5 where he played This Love with them. He absolutely smoked that guitar!
I'm a fan of John Mayer. I have to agree with Champ that his albums don't bring out the best in him, but you have to see this guy play live. He will absolutely blow you away and is definitely one of the best guitarists out there.
I know he is dying to shift away from the pop scene to make a blues/rock album. When that time comes, I know I'll be looking forward to it. Until then, I guess I will have to settle with what he has out now.
By the way, if you play the guitar and have yet to try out some John Mayer...I would recommend it. Good stuff.