Good Point : This is what I do to check on space after every install/de-install. Not sure, if this could be useful to others, but I have one small script to check this space usage before and after any install/de-install.

Few Screenshot:
1 ) After enabling the testing and extra repo. It shows that around 15mb has been used in rootfs after enabling them.

2) To make it more quick accessible I have put it in desktop shortcut. And after that its shows something like this.

You may have already got the point but jut to say that GREEN says space has been released and RED means more space is utilized.

How to use:
Run the script, it will take the pre snapshot and wait for your input. Leave this window open and then do your install/de-install. After that come back to this screen and press Enter and it will give the report.

Files attached.
chk_fs.sh Copy it to /home/user/scripts
As root
spacex.desktop Copy it to /usr/share/applications/hildon
spacex.png Copy it to /usr/share/icons/hicolor/48x48/hildon