It was mentioned on Unmannedspaceflight.com that the water plumes were measured to contain 1.6% methane. This could arise either from hydrothermal activity or microbial activity.
Anyone know if the Cassini orbiter has the ability to determine the isotope ratios of the methane?
On the Huygens lander there was a GCMS that was able to determine the methane on Titan did not arise biologically:

First 'in situ' composition measurements made in Titan's atmosphere.
30 November 2005
"From isotopic ratio measurements, the Huygens scientists obtained two key findings. The carbon isotope ratio (12C/13C) measured in methane suggests a continuous or periodic replenishment of methane in the atmosphere, but no evidence was found of active biological systems."
http://www.esa.int/SPECIALS/Cassini-Huygens/SEMK1TULWFE_0.html

Bob Clark