Re: John Mayer. Check out his second album...the live one. He does a cover of SRV's Lenny. Pretty damn good too. I was deployed in '03 when it came out and bought it off a recommendation from someone who likes guitar.
He is a genius in my opinion....he knows he plays bubble gum pop despite his influences, of which SRV is one of the biggest. He's appeared in multiple blues gatherings and shown his good chops. Yet, he figured away to break out of the local music scene where he would have remained otherwise.
To each his own, but he now plays with the best of them as a result. Eric Clapton, Buddy Guy, etc etc etc.