You can now hide apps from your Mac App Store Purchased list. These buttons do not delete apps from your Mac, they just help keep your Purchased list tidy. I suspect the buttons are a new addition in 10.7.2, but I could be wrong. Anyone on 10.7.1 or earlier see them?
If you want to restore apps you’ve hidden, go to your account area, click “View Hidden Purchases,” and click the “Unhide” button.
Just found out you can do this on the iPad too. Swipe to hide. Not working on the iPhone, though.