Among experienced guitarists, there is quite a lot of debate over the value of guitar tabs. Some say that this form of notation is incomplete because it doesn't accurately depict the rhythmic component of a given song. Most tabs just show the guitar part strung together without any indication of syncopation or offbeat patterns. Tabs are also notorious for often being incorrect representations of guitar parts. This is often true, especially with more complex songs where a particular guitarists unique approach to chord voicings and arrangement are shown incorrectly. On the other hand, many guitarists believe that they are good, unintimidating way for beginning guitarists to learn songs they like.
I personally think that tabs are a great launching point for the beginning guitar player. Once a guitar player gets more comfortable experienced however, they should start learning songs by ear if they want to explore the subtleties of the instrument.