it all depends on what you want to accomplish with the instrument...
if all you want to do is play simple folky strum-a-long songs then you can probably learn it on your own with a few books and a little help from any friend who already knows how to play...
if you're wanting to pull off something more extensive (classical / flamenco / leo kottke style fingerpicking) you might want to consider getting a tutor...
learning on your own is a good and cheap way to develop technique but it doesn't necessarily teach you how to play music... i'd been playing guitar for 5 years before i reached that point... i could play along to lots of cds (i used to pull off a mean voodoo chile) but i never really played my own stuff... then one night i was jamming with some friends and this guy came down and we started playing the mountain song by jane's addiction... but he wasn't playing it 'right' so being a bit of a bastard i figured if he wasn't going to play it right neither would i... and we launched we just played... and that was it my first musical orgasm
but it all depends on what you want in the end... there's nothing wrong with being the guy who onlly knows how to play lots of simple songs on an acoustic around a campfire (it'll get you chicks too hehehe)