Able or eligible?

Here's a chance for some of the IPKat's most knowledgeable patent people to come to his aid. In the context of last year's controversial US patent decision in Re Bilski (noted IP Finance and lots of other places too), blog team member Jeremy has been confronted with the terminology "patent eligible".  He thinks he knows what "patentable" means, which leaves him wondering whether patent eligible is

* a long-winded synonym for patentable; 

* a subtly different concept or 

* anything else.

Can any reader please advise?