Thanks for your points... Worryingly English is my first language, I'm just dyslexic. So apologies there!
Firstly let me tackle the spam RSVP point... Over the last couple of years at SXSW there has been an increase in the number of "bots" that you can sign-up to and RSVP to all events! This allows the attendee to turn up anywhere and be "on the list", which is great for them but not so great for the organiser! The organiser hasn't just put this event on as a public service, they usually want to promote their brand and product. But with the current system they have no idea how popular their event is, who is actually going to turn up and how many of these attendees are worth the marketing budget! (They may as well not had an RSVP... Which is fine, some events are for the masses!)
RocketLi.st aims to solve this by allowing everyone to RSVP with their email address (even the bots), but then incentivises those attendees who actually want to be there to carry out small tasks in return for "at event" perks (such as priority entry, cool swag, etc.)!
With regard to the tasks... We are talking about simple things such as signing up to the mailing list, following the organisers on twiter, etc. (Definitely no captchas)!
You can actually see this in action on our "test event" - http://2012closingparty.rocketli.st
I hope this has made it slightly clearer? But I definitely need to work on my pitch.