if you’re at uni, yes. if you’re not, but are still ‘young’ (at heart perhaps!), go out to events, want to share photos of stuff etc, then yeah, why not… (plus you can, in theory, keep an eye on your kids 😉 )
if, however, you are properly middleaged, not bothered about keeping in touch with loads of friends in an easy way (email IS less convenient), then no. cos you’ll just get all grumpy with it.
ime facebook at uni is almost essential – i don’t think i actually know more than 1 or 2 people who are not on it. out cycling club is organised through it, i find out about events and tickets through it etc. don’t care what people say about it, at uni, it IS VERY useful.
if my dad, however, appeared on it, i would worry (and i would limit what he could see 😉 )