This was posted a few months ago but there wasn't much info on the post and it suggested it was only for gold members.
Can confirm it is for silver (now know as free) members too and basically the points values equate to how much xbox marketplace currency you will get.http://rewards.xbox.com/my-rewards/
- the full breakdown
I've got 140 deposited so far with 20 more to come: three monthly surveys and a first time marketplace content.
How much you get will depend on whether you have renewed live before or purchased on the marketplace, etc.
But at the end of the day it's free points (the surveys take literally one minute) which are great if you're left with a small amount you want to make up without spending more money.