Out ouf curiosity, how long does it take you to respond to invitations?

Yes, no, maybe, I'll get back to you....

I tend to respond as soon as I get one, whether for a more formal-ish situation like a party where the giver has to know numbers, or even for a less formal one, like if someone shoots me a line on Facebook and invites me to a movie or the mall or something. Even if I'm not sure, I at least say that so they know that I acknowledge the fact that they communicated with me about it.

Because of that, it sends me nearly postal when people don't respond to my invitations to go for a ride or get together for lunch. I'd rather have an "I'm not sure yet" than nothing at all so I can plan my time. And I no longer plan parties. The last time I did, ten more people than I made reservations for showed up at a restaurant. None of them responded to my evite so I didn't think they were coming.

Am I alone in this? Didn't people's mothers teach them what RSVP means?