How Authoritative Is Wikipedia?

Authoritative enough for the Fifth Circuit, apparently.  Last week, in Exxon Mobil Corp. v. Commissioner (note 1), a circuit panel cited the online encyclopedia for its definition of the accounting term "accrue."  (Hat tip to Appellate Law &Practice.)

Are internet-savvy clerks are showing their influence?  Should the Fifth Circuit rely on a wiki of uncertain authorship to define a term of art?