Seriously, my experience is this: if you've got a funky phone with a built-in facebook app (iphone/android), you'll post loads of pointless updates to your wall that are of no interest to anybody, unless you care about whether someone you last saw in 1986 had dinner in Pizza Hut tonight.
OK, seriously seriously. Would you like to catch up with friends you've not seen for donkey's years? And can you also deal with re-establishing contact with all those other folk (incuding distant relatives) that you've forgotten about?
OK seriously, seriously, seriously. Give it a go. I think the pros outweigh the cons. And if you get pissed off with it, just delete your account.
And eck's got a good point - don't add folk you can't be arsed with.