After reading this post I went and got one. Ive noticed an improvement in my playing after using it for only an hour!
A metronome may be great for timing but i have to also say that as a beginner when your trying to follow the beat it makes you really notice any mistakes that you make or if you don't fret a note quite right then you find yourself correcting these things on the next 'run'.
So i have to agree with the quote
Grandslam15 - "Everyone who practices really needs to practice with a metronome."
:D