The Pubs want it to stay that way so they can stack the court, if they can ever get a President and a Pub Senate.

The Republicans for a long time now have been blocking 'two' D.C. nominees: Halligan and Srinivasan
List here: http://en.wikipedia.org/wiki/List_of_federal_judges_appointed_by_Barack_Obama

There are currently FOUR vacant seats on the D.C. Circuit
On the map at the top of the page, click where it says 'D.C. Circuit' then look over on the left side for text details, here: http://judicialnominations.org/

That will come in handy every time there's a decision in the news, and I want to know who appointed the judge.

and there are, I believe, more vacancies (4) on the DC Circuit than any other Circuit.

But the President could call Collins' bluff: there is going to be a vacancy on the Circuit that covers Maine in July. Nominate Halligan for that position.

Otherwise they would filibuster Obama's judicial nominations.

The number of judges are decided by Congress following recommendations made by the Juducial Conference. So Congress has already decided that this position should exist. Susan Collins does not get to decide on her own. She has already had her say in the matter. http://www.uscourts.gov/Common/FAQS.aspx