I downloaded an album from Amazon on Saturday night - Trilogy by Nina Simone and found it to have alarmingly low bitrates. I know Amazon do a 256kbps variable thingy, but some of the tracks were as low as 139kbps. Really poor; it's a pity they don't pre-warn you as to what you're actually getting.
To Amazon's credit, they refunded me the price (they apparently don't normally accept "returns"), and I bought the CD from them (which, oddly, was £2.50 cheaper, delivered!).
CD here, http://www.amazon.co.uk/gp/product/B0031IL61U - I wouldn't link the mp3 version, just in case!