I just bought this dress and the Quinn dress, and love them both!  They are the first items I've bought from PrAna, but probably won't be my last since the quality and fit are excellent.

As for sizing, I went with the small and it's perfect. (I'm 5'4" and weigh about 120 pounds.) One previous reviewer noted that this runs small, and it does fit a bit tighter than the Quinn dress, but the medium definitely would have been too big.  The inner shelf bra is also supportive enough for my 32D chest, and not too tight.  I love it when I can get away with not wearing a bra (especially with an intricate back like the one on this dress), and this allows for that with no "headlights" showing through.

Also, I had been worried that this Amaya dress and the Quinn dress wouldn't suit my hourglass shape and that they might look too boxy on me, but both still emphasize my curves.  The slight dip in the front panel of this dress is also nice for hourglass shapes since it doesn't create a boxy look to the front of it.

The fabric on this is also interesting.  It feels like a cotton, but I guess it's PrAna's Veeda fabric, which is a blend of recycled polyester, spun polyester, and spandex.  It has a nice stretch/give to it, and it's supposed to be quick-drying. I bought the Lake Flower Power blue color, and it's just as punchy and vibrant as it appears on my computer monitor.

I'll update my review after I've washed both dresses a few times to note how well they hold up. In the meantime, I know I'll be wearing my Amaya dress a lot this summer.

UPDATE ON 8/2/12:  I wore this dress and the Quinn dress quite a bit on a 24-day cruise we just got back from, and both held up really well.  I sent both dresses to the ship's laundry a few times, where I know they washed the dresses in hot water and dried them on high heat, but both maintained their color, shape, and size.  Now that I'm back home, I'll be washing it on delicate and hanging it to dry, but it's nice to know that the quality is good enough to stand such harsh washing.  The moisture-wicking properties of this dress were also great in hot, humid climates.