It's available today and there are pretty much no restrictions except that you have to use it before April 29, 2012. Can be used online, can be used at REI outlet, can be used on sale items.
Can be purchased here:
The fine print:
Limit 1 per person and 1 per order. Valid toward sale items and shipping. Offer is $15 for $25 to spend toward outdoor gear at REI ($15 customer paid value and $10 promotional value). Paid value does not expire, promotional value ($10) expires: April 29, 2012. Offer valid at REI stores, REI Adventures, REI Outdoor School, REI.com and REI-OUTLET.com. Nontransferable and not redeemable for cash, except where required by law. Not valid for previous purchases. Will not be refunded or replaced if lost or stolen.