Expanding a bit on what MGS said...
-beginning in 2012, the miles have an expiration of a year (or smt like that)
-you can use these to raise your EQM up to 75k. If you come 'close' to a level (below 1k, as mentioned) they can be used to bump your EQM up so you earn the level
-In 2011, it was possible to use them to bump to 1k. Several of us did this rather than take a short mileage run
-in the past, if you redeemed these it counted towards both your EQM and lifetime miles. I assume it still counts towards lifetime, but don't know
-flex miles earned previous to 2012 did not (and do not) expire. I don't know what this means for those of us with pre and post miles...I've got lots of pre-2012 miles and I've already earned some post-jan 1 2012 fpqm. Hopefully if I earn X fpqm miles in 2012 I will be able to transfer X fpqm to my account...raising my lifetime miles by X...and not 'lose' the earlier miles which don't expire. This is the hope of most 1Ks who have the pres plus card, I think...
-lots of us who are 75-99k a year milers were upset that we can not use these to hit 1k in 2012 and beyond. Haha...at the same time, 1ks who are 150k plus a year were upset that us 'lightweights' were able to do this in 2011