According to Tim O'Reilly, sales of PHP books are up 16% in the last year. C# sales are also up slightly. While sales of other language books are down, Python continues to gain on Perl. My sense is that trends in the MapServer community roughly parallel the trends in computer language book sales.
Perl was the original mapscript language, followed soon after by Tcl and PHP (3). Use of Tcl mapscript has, as far as I can tell, ceased. O'Reilly makes no mention of Tcl in his article. Over the last year use of Perl mapscript has eroded (measured by user and developer list traffic), with users moving to PHP (4), Python, and Ruby. Use of Java mapscript continues to grow very slowly. MapServer's C# interface is attracting much more interest in the past year. This appear to be an entirely new set of users that are not crossing over from another mapscript-ing language.
Interest in PHP mapscript, already huge, continues to grow despite the lack of clear breakthroughs for PHP 5 or DSO support. It's easy to understand; PHP is pervasive, well documented and promoted, and (my bias may be showing) how is a PHP shop going to migrate its applications anyway? To Python? How would they pick from the many frameworks? To Java? They've chosen PHP because it is easy and flexible, and would struggle to shoe-horn their apps into a Java framework. There are new PHP applications and there are legacy PHP applications, but I can't imagine any moving away from PHP.
In the next year, I expect the Perl -> PHP trend to continue for MapServer. Java mapscript users will probably be switching to packages from the maturing GeoTools/GeoServer/uDig nexus. Python users will probably be switching from mapscript to PCL. C# developers, who now seem to be entirely in the Microsoft rather than Mono camp, may be picking the Carbon project over MapServer. I'm looking forward to the meeting this summer and the chance to hear other takes on the linguistic landscape of the future.