Cairo is the “next generation” vector graphics library for Linux and very cool to have it available in PHP. Also cool about the extension was created using PEAR::CodeGen_PECL, which Hartmut describes here: look Mum – no C! (well almost).
This raises the question of whether it’s time to depreciate GD? As far as I’m aware, it and the PCRE extension are the two main problem children preventing PHP from being thread safe. It may be possible to replace PCRE and preserve backwards compability, with ICU regexes, which claim to based on Perl’s regular expressions. Dropping GD would be much more painful but with Cairo and the imagick extension, there might be enough to keep everyone happy. This is in the interest of running PHP under Apache mpm. Would be interested to hear thoughts / opinions on how realistic that is?
Side note: my dumb view of the difference between GD and imagemagick is the former is more for image creation while the latter is more for manipulating existing images.