Mayor orders MANDATORY evacuation of low-lying areas (Zone A) & all of the Rockaways by 5pm Saturday.
The main information about Hurricane Irene preparedness & possible evacuations can be found in two PDFs: the hurricane brochure (750kb)
and the map (1.5mb).
There's also a Flash-based viewer of this PDF map.
This website was created as a backup for information on NYC.gov, but NYC.gov should still be treated as the authoritative source.
You can use irene.betanyc.org as the URL to access this page.
Hurricane Irene at CrisisCommons, particularly the NY Page
Google Crisis Response