Every since graduate school when a member of my dissertation committee lit into a draft paper of mine I developed a healthy pet peeve about the word "data" (the plural form of the singular "datum" -- or so I thought). Over at the Social Science Statistics blog Mike Kellermann's recent post gigs into the usage wars waged over data and uncovers some ambiguity.
Mike appears to throw his lot behind the "data is a singular because it is increasingly view as a 'mass noun'" camp. For me, however, Strunk & White's classic and time-tested The Elements of Style breaks any usage "ties." Regrettably, even here, while the tie is broken, a hint of change exists. "Data. Like strata, phenomena, and media, data is a plural and is best used with a plural verb. The word, however, is slowly gaining acceptance as a singular."