It's a great observation — worth mentioning in a proper post and not leaving to the comments. Psalm 1:1 is one such "contentious" verse; however, the translators were somewhat further along in Psalm 1 the day I observed them. So I can't give firsthand insight into the discussion that took place.
However, for those interested in reading the translators' "official" rational for using plurals to translate singulars, one of the committee members has provided a very thorough discussion of Psalm 1:1 on TNIV.info. (Note: You have to scroll down a bit to get to it.)
I won't add anything to their explanation except to say it's well worth reading.
Last, something Wayne wrote in the comments section about singulars and plurals deserved to be mentioned here, because it's so good:
All Bible versions, including those which are essentially literal and those even more literal, such as the NASB, have had translators that recognize these facts, which show that forms do not always match up with meanings one-to-one between languages.
I, for one, am glad that all Bible translators have recognized this. I'm glad that the KJV, RSV, ESV, NASB, HCSB, NIV, TNIV, NLT, and other versions translate elohim as "God" when it meant "God" in the original texts, even though it was grammatically plural.