Just got my new pair, and for ME the secret was to go two sizes up.  I am 5'4" and weigh 145... according to the chart I'm a B... but the C was even too small for me.  Just got the D, and bingo!  Perfect!  Doesn't seem to roll, and I might actually be able to breathe in the thing.  Those who haven't been happy before, try going two sizes up... worked for me~ five stars now!

My previous review:
I am completely torn about my rating on this one.  On the positive side, this product shaves ten pounds off my appearance, easily.  So five stars for that.  Two negatives though...  First, I ordered a size up (from what is recommended at Spanx.com), as everyone seems to suggest.  They are still VERY tight, and still roll down.  Secondly, I have not even worn them yet... I only tried them on twice with my Maid of Honor gown... maybe had them on for a total of fifteen minutes each time... and all of the stitching on the waistband started to come out in a big, long unravel.  It happened in two different places on the waistband.  If I hadn't bought them so long ago (well in advance of the wedding), I would have returned them and requested a new pair.  Now, I'm here to order another pair, and I think that this time I'll try ordering two sizes up, and see if that stops the rolling problem.  I will save the second, damaged pair as a backup for the wedding day.  Those two issues caused me to take away two of the five stars that these could potentially be (for me, anyway).  One more thing... as it stands now, I couldn't imagine wearing these every day... it really is a GIRDLE!  But for a special occasion, or a night out on the town, yessiree!!  They do really suck you in and give you that figure you wish you had! (Maybe not recommended for going out to dinner, if you plan to eat more than a salad LOL!)