My problem is that the appstore launches itself if it's not running. I have tested it multiple times. If you see it running and go into applications management and force stop it it'll shut down for a while then, a while later, it will open back up and be running in the background again. Even if you never launched a single app in the meantime.
I just tested it again while reading this thread. In the time it took me to read the whole thread I force-stopped the amazon store app at the start of the thread and by the time I started posting this reply, sure enough, it's running again. Chewing up approximately 10mb of memory.
I don't mind it being used as DRM but if I'm not running an app that I downloaded through them (I'm not, I only have 1 app purchased and it was angry birds) then there should be no reason whatsoever for the app store to be launching itself in the background. DRM or no DRM it has no business tossing itself active every little while and, I'm sure, hitting my internet connection.
Since installing the app store I've noticed that I have about 10-15% less battery life as well. So the hit isn't insignificant.
I've uninstalled it to save myself battery time. Just not worth keeping it installed if it's going to constantly launch itself in the background. I'm assuming it is also pinging the web for DRM information when it does that.