What must laws must one amend a retirement plan after 12/31/06?

Actually, of course, the Pension Protection Act comes to mind.

http://www.irs.gov/retirement/article/0,,id=165131,00.html

http://www.irs.gov/pub/irs-tege/ppa_chart.pdf

If anyone recalls matters regarding the finer points of these amendments, feel free to reply.