sry but i dont really understand your english.
you had after uninstalling a app less space in rootfs then before?
here some points how you can free your rootfs:
1:stop installing extras/devel trash i guess you heard the thousand warnings
2:uninstall apps you don´t really need
3:some apps let trash on your device even after uninstall.go to xterm-type root after that apt-get autoclean and apt-get autoremove.then type reboot and look how its going.
if this all doesn´t help you here are some tipps from the wiki:
http://wiki.maemo.org/Free_up_rootfs_space