I remember reading about the study last year that failed to find sodium in the Saturn E ring with Earth-bound telescopes, suggesting Enceladus could not have a subsurface ocean:

Sodium issue clouds Enceladus.
By Molly Bentley
Sunday, 16 December 2007, 17:21 GMT
http://news.bbc.co.uk/2/hi/science/nature/7145530.stm

But I don't remember seeing this study this year using the Cosmic Dust Analyzer on Cassini that did detect sodium in the E ring:

Saturn's moon may host an ocean.
By Ron Cowen
August 30th, 2008; Vol.174 #5
Enceladus' geysers could have delivered sodium from its underground ocean and into Saturn's E ring.
"The Cassini spacecraft has found what may be the strongest evidence yet that Saturn’s tiny moon Enceladus has an ocean beneath its icy surface. If the liquid water finding is confirmed, it would suggest that the moon may be one of the most promising places in the solar system to search for signs of past or present extraterrestrial life."
...
"Cassini researcher Roger Yelle of the University of Arizona has a different view. "The surface of Enceladus is not pure water ice. We just don't have a good idea of what the other components are," he notes. "There could be a small amount of sodium in the minerals in the surface layer." The sodium detected in the E ring could have come from that material on the moon's surface, rather than from its interior. "I don’t believe that you can say that the detection of sodium [in the E ring] implies that it came from a sub-surface ocean" on Enceladus, Yelle says. "So, let’s not run around crazy-like claiming the likely detection of life because sodium was found in dust particles in the Saturn system.”
"Another complicating factor is that studies from Earth, using large telescopes such as the Keck Observatory atop Hawaii’s Mauna Kea, have not found any sign of sodium in the E ring. Nick Schneider of the University of Colorado at Boulder reported the lack of sodium last December in San Francisco during a meeting of the American Geophysical Union.
"But such studies, notes Kempf, can only detect sodium in its gaseous form, not the solid sodium in the frozen ice particles. He maintains that the bulk of the sodium in the E ring lies in the solid phase recorded by Cassini’s cosmic dust analyzer."
http://sciencenews.org/view/generic/id/34109/title/Saturns_moon_may_host_an_ocean

The Cassini sodium readings will also be presented at the upcoming December AGU meeting:

Sodium Salts in Ice Grains from Enceladus' Plumes: Evidence for an Ocean below the Moon's Surface

Bob Clark