Yes... you get junk mail. I get about 600-700 a day. But, since i didn't use my regular email, I dont care.
I don't do the websites that need you to refer to 20 friends... i do the DIY ones.
If the OFFERS ask you for a credit card, then go ahead. You are paying to do a trial or a sample of some sort. They are just normal companies doing trial offers and using these "Freebie" websites for advertising. For instance, one of the offers is Netflix. Netflix isn't a scam... its just another company doing advertising.
To do these, you MUST be willing to spend a little cash. Its not a completely free thing, but hey... I spent $20 for a $500 gift card. So, I made $480 profit. I spent about $50-60 for a $700 laptop. I'm going to sell the laptop and get more back.
EDIT: Here is an easy one. This is similar to one I did. Complete 6 offers
http://consumerrewardzone.com/?cid=WBnjstPPpKI&u=fcad40b53ab8ba231693acf7d14e8620&s=94.
If there is no time limit (read terms and conditions), then if there are offers you don't want to do such as credit cards or expensive ones, then you can come back at a later time and check to see of the offers have changed... and they do. I started my laptop one and got to the last page and found "OOD's" or Offers Of Death. I waited a few months and they changed to a $10 30 day trial and a Relasom sample which only charged $5 shipping for a 7 day trial.