Thanks to those who have tested it (and/or will test it). The results where helpful and resulted in Bug#548443 filed against localepurge and GNOME Bug #596429 against glib. The first one is a case where quotes where used inside a value, although this has never been defined to work, and the second one is a problem with GLib’s GScanner not ignoring multi-line C-style comments although it was configured to do so.
I also fixed some bugs in APT2, like the missing build-depends on libgee-dev and the configuration parser now accepts ‘.’, ‘_’, ‘+’ in the option name. I also talked with Eugene about some differences in the way cupt and APT2 handle quotes and about some other parts of the configuration format. Seems this was a good day.