After you're in, there's no simple way to say "leave me out of this." Sure, you can ask to be removed from the guest list, but you're still forced to waste your time on their intrusiveness. Its like being polite to telemarketers.
Last time, it took me 6 emails, and finally they got it. I don't receive "evites" at all. If you put me on your event list, I disappear. That's the way I like it. Sorry, this makes it extra work to invite me to your event. Or I may even silently miss it, because I don't see your "evite."
But I decline to be an eyeball in evite's world.
If you ask very nicely, I have an email address that you can use. I don't use it for anything else. I ask that you just use my first name with this address. However, you still lose points for using it.
Please take a look at Evite Alternatives for some other services you could use.
[Update: Here's the data they're selling about you when someone else opts you in: "Evite: A Buyers Guide."]