To anybody who is thinking about paying for rubies on Tetris Friends, I just did one of the free offers which was extremely easy and netted me 250 rubies (~$17 worth of rubies). I think this offer is only available to people from North America, or U.S. citizens, because Wojtek didn't see it on his choices.
Look for the "Yahoo Personals" offer. The signup is pretty easy but needs a credit card and your address. It's a 7-day trial before they charge you money, so make sure you cancel within that 7 days. This one credits after 1 day rather than instantly so after completing it just wait a day like I did before cancelling. I even used an empty American Express gift card and it worked fine.
Cancelling is very easy and can be done online: http://help.yahoo.com/l/us/yahoo/personals...ervices-07.html
There's another offer which is very easy as well, Netflix offer gives a free trial and then charges afterwards. Once again, you can sign up for it, receive your 175 rubies (confirms instantly), and then cancel. With this offer, you won't be able to use prepaid cards however.
Cancelling for this is also easy and can be done online: http://www.ehow.com/how_5019103_cancel-net...bscription.html
Okay, thats it.