apt-get automatically does the dependency checking before providing the list of packages that will be removed. so in your case:

liblongcat0 -> ok to remove (installed from extras-testin)

the following are the qt libraries that were going to be removed. its safe to remove them because they are available from the repos.
libqt4-maemo5-core
libqt4-maemo5-gui
libqt4-maemo5-network
libqt4-maemo5-opengl
libqt4-maemo5-phonon
libqt4-maemo5-webkit
libqt4-maemo5-xml
libqt4-maemo5-xmlpatterns

Something odd has happened.

I had 17M free through reboot. After running apt-get and answering no (as posted) I humped to 23 then 28. Does it do something by just bein launched? maybe a stuck daemon? Odd.

Anyway, ran autoremove:

Do you want to continue [Y/n]?
(Reading database ... 25544 files and directories currently installed.)
Removing liblongcat0 ...
Removing libqt4-maemo5-webkit ...
Removing libqt4-maemo5-xmlpatterns ...
Removing libqt4-maemo5-phonon ...
Removing libqt4-maemo5-opengl ...
Removing libqt4-maemo5-gui ...
Removing libqt4-maemo5-xml ...
Removing libqt4-maemo5-network ...
Removing libqt4-maemo5-core ...
/home/user #

Nice.
DiskUsage reports 28 M free. Rebooting...

DiskUsage reports 32.1, root 36.3

Didn't exctly free 42M, it lied to me .

The difference was opted, right?

Already zero.

the rootfs is compressed. so you wont see the 42mb freed off it. glad there is now more breathing room in your device.

if someone were to accidently delete the "partial" folder and "lock" from /var/cache/apt/archives/ what would be the consequences?

I have no idea what I'm saying but since downloads resume I'm gonna guess that's what the partial is there for. In which case, no resume on already-partial downloads. Aka, nothing.

Also, like many other apps, lock files are the Unix equivalent of the Windows' one-instance mechanisms. I'm guessing it'll recreate next session or can't delete if a session is in progress.

Should I be hinting people when I'm not sure myself? Don't answer that. But since removal has been suggested already and it is a cache, after all, I'm voting for safe.

Oh it's at it again.
I'm down to 17 M, again.

I installed and removed two apps, both claiming 180K range.

The autoremove claims that it has nothing to do.

dpkg listing of packages is even more confusing now, as it lists packages such as libqt4 as large, but not installed:

dpkg-query -W --showformat='${Installed-Size;10}\t${Package}\n' | sort -k1,1n

--snip--
7856 hildon-theme-alpha
8032 nokia-maps-ui
8868 libc6
8884 dtg
9780 python2.5
11692 libqt4-maemo5-gui
12292 microb-l10n
13276 libqt4-gui
13584 cmt-firmware-rx51
15640 microb-engine
16304 posix-locales
16576 libicu40
18252 libqt4-maemo5-webkit
18612 mplayer
20744 libqt4-webkit

Great. Let's see:
libqt4-webkit

/home/user # apt-get -s remove libqt4-webkit
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
libqt4-opengl libqt4-phonon
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
googlelatitude libqt4-webkit
0 upgraded, 0 newly installed, 2 to remove and 17 not upgraded.
Remv googlelatitude [0.3-9]
Remv libqt4-webkit [4.5.3~git20090723-0maemo4+0m5]

Ok, so it's in use, but no sweat, I had GLU before this began and I had 32M left. I skipped MPlayer because I want it and because it's optified anyway (i read that around).

Next it's libqt4-maemo5-webkit. Cue confusion:
/home/user # apt-get -s remove libqt4-maemo5-webkit
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libqt4-maemo5-webkit is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 17 not upgraded.

It's not there. Same goes for libicu40. I'm fairly sure posix was there by design, so where's my space?

Rebooting did nothing. I'm thinking a file system diff is my last chance. Since I know little about the OS, I'm thinking ls -R /> today.txt and then export the txt back to my Windows. Do this after a sudden increase and catch the files.

Anything less ... hacky?