I don't think Pink Floyd is overrated at all- they're not the best, but they put a lot of good stuff out. Simply put, many people equate them with Another Brick In The Wall, or Dark Side of the Moon.

The Syd Barrett era of Floyd, no matter how short-lived, had wonderful psychedelic music. Piper at the Gates of Dawn, and Saucerful of Secrets are great psychedelic albums.

Most of the people (not all) who classify Floyd as overrated usually have only listened to Dark Side Of The Moon and The Wall. In my opinion, those aren't the best albums... Meddle, Wish You Were Here, Echoes, and Animals have amazing guitar work. Have you heard many other artists like David Gilmour play with such clear-cut sound, and genuinely beautiful notes? He may not play speed guitar like some of the more modern nu metal bands, or even classic metal bands, but he uses very euphonic techniques. Instead of just playing a random list of semi-related songs, they use concept albums, which can have amazing potential.

I don't think the Beatles were VERY overrated, a lot of their original material was stifled by Phil Spector- Let It Be... Naked is a good example of the stuff they really wanted to put out. Not the best band in the world, but I really like their stuff.

As for jam bands, like Grateful Dead and The Allman Brothers Band, their fanbase is mostly people who followed their shows for a good time, not just the music. Jam bands are more of a background kind of music for having a good time, not for people to claim 'they're the best band EVER.'

I think Elvis is definately overrated. He was more of an image who borrowed a lot of his riff structures and singing styles from early black American blues/jazz underground music, and made it feel more acceptable for white people to listen to.