Certainly they help you learn faster. Everything I know has been picked up from random discussions, sites like this on the internet, and from just trying stuff out.
Sometimes I just wish I had someone to explain everythin properly to me - I expect I have loads of bad habits that any decent gutairist would shake his head in disgrace at!
At the mo, I'm trying to teach myself some lead style - but it took me a couple years really to teach myself rhythm - learning everything the long way. However it's helped me develop my own style.
I think also with lessons, it's easier to see the improvement, and your progess is better regulated. I might try really hard for a bit til my fingers hurt and then not play for ages - I don't want to damage myself. Sometimes I get discouraged and think I'm gonna be rubbish all my life - one of those old men who thinks he can play the geetar!
So yeah - If you've got the time and money for lessons go for it. It also helps if you're a nice person as well. I tend to be a bit -'don't tell me what to do'!!!!
JE