just re-flashed my device yesterday, and apart from the default repository i have only enabled Extra's. As i installed each app im monitoring rootfs space, and if after an app install's a significant amount is used i do an apt-get clean and reboot.
I've noticed 2 app's so far in the Extra repository out of around 10 i've installed are taking a bit of limited rootfs space.

touch search (2.1-2) 2mb
extra decoders support (0.3.4-1) 3mb

could someone more knowledgeable test this , as i build my N900 up to where it was pre flash i've add more app's from extra's, testing and dev i expect them to use rootfs.

Yep apps in Extras (not necessarily -testing or -devel though) are optified.

http://wiki.maemo.org/Help_testing_s...esting_process

You've got to differentiate between the apps themselves and their dependencies. There doesn't seem to be any easy way to optify libraries, so any shared libraries installed will use up rootfs space.