I agree with most of the comments from others. I've been with them for about 4 years (I think).
The only kind of downsides I've experienced were the price cap on your selling price (currently $29.95, but they tried to convince everyone to go even lower a little while back), and the loss of your branding. They use their own generic template for the dvd covers and throw on some of your screen grabs. And unless you specifically tell them you want your own artwork used, those covers will then show up on AEBN when the dvds go up there. And even then, I've caught them being changed back to the AMVC covers.
They are very professional about getting checks out on time, invoicing, following through with communication, etc. But in my experience there doesn't seem to be much of a personal connection. Not like I wanna be best friends, but in all the years I think I've only talked with them on the phone once. All communication is documented via email. Which may be a good idea, but is a little sterile feeling.