I received these yesterday.  I'm 5'8", 140 lbs.  Normally I wear a size 5, but after reading the reviews to order a size larger, I did just that and ordered a large.  Overall they fit pretty well, but the waist is a bit large so I find myself hiking them up quite a bit today. :-( I'm hoping they'll shrink a bit after washing them, but if not the waist could be sewn to be a bit smaller.  They are extremely flattering, and a really nice soft & stretchy material.
I'd be curious to know if anyone with my height & weight ordered a medium & if they fit better then the issues I'm having with the large.  I'm thinking of ordering a couple more pairs if they're available.