From the forum annoucement:

The -nolisten, -noupnp and -nodnsseed command-line
options were renamed to -listen, -upnp and -dnsseed,
with a default value of 1. The old names are still
supported for compatibility

but that's only true on the command line, not for bitcoin.conf options.

I have a bitcoin.conf with "nolisten=1" in it, but it's being ignored.

The "interpret -nofoo as -foo=0 (and -nofoo=0 as -foo=1, as long as -foo not set)" code is in util.cpp's ParseParameters() function and runs before the bitcoin.conf file is even read.

This breaks existing configuration files, so it's probably best to fix this before the release of 0.6.