LukeW Interface Designs have a very interesting article on Discoverability of rich web interactions. How could we know that there is drag and drop feature here or there ? There is some great proposal for solution to make it looks better like displaying bubbles with help message, changing cursor, arrows ..
Many implementations of rich Web interaction designs encounter issues of discoverability. As I pointed out in Bringing Desktop Interactions Online, the awareness of actions like drag and drop and multi-select within Web applications is often low because people don’t expect these behaviors to be possible. As a result, designers often include messaging to educate users on what’s possible.
