I don't really get the anti-facebook people.
It's a really effective and communicative tool to use to remember friendly acquaintances that are of some important reference, it is good for continued communication with old friends and current friends. It's great for getting messages out and passing information to large groups of people. It's nice to be able to see what a friend is up to without having to invest too much time in them due to schedules and such. I use it daily for about an hour (non-consecutively) to just chat and get messages.
To a certain extent, it's a phonebook, text message, internet messaging, platform sharing, schedule book.
If anything, the practical value of Facebook for event-invitation is useful.
It is your choice to use it or not, but I can't see the downside of having an account that you just semi-regularly check on. It's mere minimum effort to go get one.
I have 301 friends. I message/chat/comment with about 70 at least once a month.