I've installed a bunch of apps from the App Store, some free, some paid. Many of them are garbage, were uninstalled, and I don't intend to ever install them again.
How can I remove (or hide) them from the "Purchased" list?
I am running Lion (10.7.2), and there is an x just to the left of the Install / Installed button when you hover over the item in the purchased list. Click it for each App you do not want listed. I don't believe this uninstalls the App, merely removes it from the list. I did this to a program I actually wanted in the list, I don't recall even being asked for confirmation.
Now as far as getting a purchased App back onto your purchased list, that is another issue, and another question.
Right now, there is no way to remove purchased apps. It's very annoying, hopefully will be possible in the future.
You may hide purchases in OS X by hovering over an item within the
Purchased tab...hold Ctrl+right-click, then select "Hide Purchase".