Hello,
everyone. I never tried a sweepstake offer so far, and that has to change 
But before i can do that a few questions arose - pretty newbie stuff, unfortunately...
As i understood it, Sweepstakes are the 'Win an iPhone', 'Win Vouchers', 'You have been chosen ...'-type of offers, right?
Why are they called sweepstakes anyway? Is there a reason for that?
To set one up i would need a lander and a traffic source like zeropark, right?
Are other traffic sources than pop traffic also good for sweepstakes and if yes, why?
I assume cheap traffic (pop traffic) is good because there might be a lack of user intent with sweepstakes so we follow the throw-stuff-to-the-wall-and-see-what-sticks approach?
The landers are mostly the questionnaire-type of landers, is that correct?
So we try to get people to sign in to something. SOI or DOI?
In theory: We say user can win something on lander, if he answers some questions / or gives right answers to questions. User answers (most dumb question ever) on our lander correctly and is redirected to the offer-landing-page. He signs in and our conversion happens (SOI)?
That's it. Would be glad if someone could give a few hints, please :-)
I would also appreciate if someone would answer these questions 
Sweepstakes have been around for foreverrrr and is probably one of the most stable verticals in AM through the years.
To answer some of your questions...
As i understood it, Sweepstakes are the 'Win an iPhone', 'Win Vouchers', 'You have been chosen ...'-type of offers, right?
You are 100% correct.
Why are they called sweepstakes anyway? Is there a reason for that?
http://en.wikipedia.org/wiki/Sweepstakes
To set one up i would need a lander and a traffic source like zeropark, right?
You CAN direct link, but best practice is to use a lander. For me personally a questionnaire lander has always worked best compared to other prelanders. Zeropark is def. a good source, but this is a vertical which works on any source really. Don't forget about the Google Display Network and Facebook either.
Are other traffic sources than pop traffic also good for sweepstakes and if yes, why?
Sources like Zeropark and 50onRed are especially good since you can target well here (e.g. if you promote a grocery voucher sweepstakes, target supermarkets). Other sources are Google & Facebook.
I assume cheap traffic (pop traffic) is good because there might be a lack of user intent with sweepstakes so we follow the throw-stuff-to-the-wall-and-see-what-sticks approach?
Pops don't necessarily have to be cheap. What's being run a lot on pops though is they browser survey style landers. For pops in general you need a higher budget than other traffic types.
The landers are mostly the questionnaire-type of landers, is that correct?
Correct
So we try to get people to sign in to something. SOI or DOI?
You want people to enter their details. Some offers are SOI while others are DOI. My preferrence is always SOI, since then I'm not dependent on the email delivery skillz of the advertiser.
We say user can win something on lander, if he answers some questions / or gives right answers to questions. User answers (most dumb question ever) on our lander correctly and is redirected to the offer-landing-page. He signs in and our conversion happens (SOI)?
Yes this is true. Be careful with how you write your content. Always imply the user has a chance to. Me and words like "might", "may", "possibly" are my best friends when I create this prelanders.
Any other questions? Shoot!
Thanks for your answers so far!
What are the most common ways for sweepstake owners to monetize their leads? I saw offer walls with magazine subscriptions right after signing up. So are the offer owners affiliates too? Do they also follow up long-term through email marketing, retargeting, etc?
Do the prizes really get delivered? Or are some of these offers flat out scams?
I'm pretty sure one of the thousands that subscribed gets the prize, it's a peanut compared to what they earn on every subscriber.
I used to do sweepstakes for many years, but the trend lately went down mostly because of country regulations on mobile content.
It's hard for me to find good converting offers, mundomedia used to have a lot of them, today just a handful and only 1-2 countries bring most of the conversions.
Which networks you guys recommend that have different GEO's for converting sweepstakes?