I love facebook, it's a fantastic creation and the main appeal for me is that it's so universally used by all ages, all backgrounds and different levels of IT (or any literacy)
As a normal bloke, it allows me to keep in touch with friends and family, share photos, videos and see the same from others - again, other websites do this better, but I don't have people from all areas of my life accessing other websites. With Facebook, they're all there already.
As a comedian, it allows me to have a fan page, promote myself, update people with my next gigs, upload videos of my performances, promote my own comedy night with a seperate page and link them to my comedian page and the page for the venue. It links me with other comedians, over 100 odd other acts are now 'friends' and I've recently emailed 1700 comedians to offer performance spots, in one go without hassle. I've also got an entity as a comedian which agents/promoters can check out without running my own website.
The downsides being the spam and junk from idiots and apps, but you can just hide those, problem solved.
It's also one of those things that's cool to hate. The haters are just missing out