Originally posted by trebledamage
A musician should know how to read music . . .

This is the crux of the problem. Most guitarist aren't musicians (in the strict sense of the word). If you were to ask 100 guitarists if they considered themselves musicians, 95 would probably say - "Hell no, I'm a guitarist."

I can't site read, but if you give me a sheet of music I can sit down and figure out how it's supposed to go. The importance of site reading depends on your musical goals. If you just plan to play in a rock or blues band, then learning to read music would be pointless. If you want to get into jazz or classical, then it would be a good idea to learn. You can get by on tabs for a while, but you'll need the music eventually.

Tab is so popular because it's an intuitive system for the guitar. If you take a piece of sheet music for guitar, you have to spend a lot of time working out all the fingerings and note placement (because there are many different iterations of each note on the guitar). With tab, you know right away what the fingerings are and which position you're playing in.

So there's a trade-off. Tab tells you exactly where to put your fingers, but doesn't tell you anything about rhythm. And vice-versa for sheet music. Sheet music was created by the order of the Pope sometime in the early middle ages, before the guitar even existed as an instrument, as a means of recording music for future generations.

It all depends on your goals as a "musician".