I had the same dilemma just yesterday. I had contacts that were just emails, either from facebook or yahoo (I think). I couldn't long press and delete like a regular contact so I just ended up linking them to the facebook or google contact I already had since most were already on my phone as regular contacts. This made my contact list a lot cleaner.
Would be nice to know if there was a way to just delete though.
Just set the phone to not display the contacts for which you have no phone numbers. In your contacts list, press the menu button, choose view, and check the box for "Only contacts with phone numbers." That's what I do.
^^Thanks for the help everyone. I just did the one that said show only ones with numbers. There has to be a way to delete those ones some how. I did try going into google but there not even there. Thanks everyone.