As Josh notes, there's been some confusion out there regarding extensions to the grand jury looking into the CIA Leak Scandal.  I saw Keith Olbermann say that the Grand Jury cannot be extended beyond tommorow.

The answer is yes it can.

There are two types of Federal Grand Juries, Regular and Special.  The journalists aren’t looking at all of the applicable statutes and rules when they say it can’t be extended.

Generally, Fed.R.Crim. P. 6(g) provides that a Grand Jury may serve no more that 18 months.  A judge may extend this term up to six months.  It may not be extended by more than six months except pursuant to statute. 

However, special grand juries are empanelled under 18 U.S.C. Chapter 216.  Specifically, 18 U.S.C. § 3331(a) provides that a special grand jury may be created in any district with more than 4 million inhabitants or where the Attorney General or several of his designees determines it is so needed.  These grand juries can last up to 18 months and may be extended in six month periods up to a total time of 36 months. 

Special grand juries are called to investigate a particular crime, usually one that is of some importance. Special grand juries are convened for a period of 18 months, and may be extended for six month intervals for a total of an additional 18 months. 

From the reports I have seen, and from pure logic, this is a Special Grand Jury.