yah, I've been using it since around january, got in through a promotion where they lowered the price to $4.99/disc(although they're moving it back up to $5.99 this month). the site is pretty good. they use media mail for free shipping(although it's never taken longer than a week for a cd to get to me).
selection is alright, but they're missing some big stuff(beatles and pink floyd off the top of my head). they don't really have true indie stuff, but they do have a lot of niche artists. I love the queue system they have, useful if you're forgetful like I am. also, it's $5.99/disc, which can be good or bad(good for buying multi disc sets, bad if you're buying something with a crappy second bonus disc).
I think if you work the main BMG service you can get CDs for ~$3-$4 though, but I'll pay extra and avoid the hassle that comes with it. my main complaint is that I wish they'd add more stuff more frequently, but oh well.