There is a lot of code written in PHP4 which is considered stable.
December 2007 is the development support end deadline. Mid-2008 is the security support end deadline. Which means from now to end of 2008, PHP will be in a state of flux. At least one web portal can come up with the single theme being PHP4 to PHP5 conversion.
The year after that, the same will repeat with PHP5 to PHP6.
I suspect this will give about 4-5 really good portals and more crowded migration sub-portals at existing PHP community sites.
Code migration, analysis, redesign, security re-tesing, audits, lots of work.
Looks like lots of work and good money to me.
Start learning PHP if you haven’t yet.