As great as Facebook is for a lot of things, I don't use it for event invitations.Of course there are exceptions to this, but in general, Facebook's capital-E Event feature doesn't get people out to your real-life event.
Here's why :
Facebook doesn't send reminders. Maybe they'll fix this, but right now it's easy to lose track of invitations unless you regularly check your event schedule.
It's sometimes used for events that don't require being there in person. You've probably gotten these. They're for things like "A moment of silence to commemorate _______ " or "Christmas, wherever you are," or "BOYCOTT _______." Which is fine, but those items make it less of a list of conferences and happy hours and things you attend in person, and more a list of things others want you to think about. It clutters up your "event" list with different types of infomation.
Facebook users are unclear on privacy settings and expect a default towards making too much information public. Something I hear all the time is "I don't want everyone knowing my entire schedule."
Not everyone is on Facebook. For every event I organize, there are at least a few non-Facebook users I want to invite.
A couple of the alternatives that I like:
Evite.com is the original — I think I started using it in 1998. It used to be great, then it looked really dated for a while because they didn't update their template designs, but now it's much better. They have always allowed registered users to include multiple email addresses, with one set as the primary and notifications go to the primary address. This means that if you registered an address for a job you no longer have, you'll still receive invitations that are sent to that address as long as your primary one is still good.
You can allow guests to invite others, you can take polls (for example — have your friends vote on a restaurant for a group dinner) and you can allow them to choose items to bring (for, say, a potluck).
Pingg.com has Evite-like features, some beautiful templates and also allows you to sell tickets for events (their fee is $1 per ticket plus Paypal transaction fees).
Both allow you to show or hide the guest list.
Maybe you still want a Facebook option, because you might not have an email address for everyone you'd like to invite. No problem — after you create and send your Evite or Pingg invitation, you can share it on Facebook.