www.bckstgr.com

Through 1/31/13 earn up to to 600 miles for registering
and linking to Facebook, Twitter and Foursquare.

My son found this site yesterday - sent me a text that said "Dad, you always like these things where you get miles for free".

Very easy to register and to link my facebook, twitter and foursquare accounts - You get 200 miles for each x 3 = 600 miles. I have secondary accounts set up on all 3 for these sort of things.

The miles posted instantly into my MileagePlus account - very easy way to extend expiry date by 18 months to July 2014.

When registering, you need to give your MileagePlus PIN - I first changed my PIN, registered using the new PIN, received the 600 miles, then changed my new PIN back to the original PIN.

There are additional earning opportunites by Tweeting or Liking on Facebook - I did a few as a test, and quickly earned another 110 miles - which again, posted immediately.

There is a BCKSTGR thread in the MileagePlus forum where posters say they had delays in getting miles to post - this was back in December - perhaps some teething issues.

At the moment, the site seems to be working very well, and a quick miles top up. Enjoy.