I am running Natty and I have the trashcan applet in one of my panels in Gnome and when I drag items to the trash can they get put into the panel instead. I can still put things in the trash can by right-clicking on them and moving them to trash. And I can click the trash can to view the items in it and empty it, but it always shows as full.
One suggestion I have would be to check for hidden files within the trash can by pressing Ctrl+H to show these hidden files. As far as dragging items to the trash can, this is a good idea and you might want to propose it do someone who develops the Unity interface. You can find them on Launchpad here: https://launchpad.net/unity