I think the easiest way to find out what packages came with something like kubuntu-desktop (or any other package) would be to check out http://packages.ubuntu.com/. This gives you a detailed listing of everything that is required, recommended and suggested for every package available via the offiial repositories.
For 10.10, the kubuntu-desktop package is located here: http://packages.ubuntu.com/maverick/kubuntu-desktop
If something is marked "depends" it is required for the package to function correctly. If it is marked as "recommends" then it is installed by default, but not required (apt-get install --no-intstall-recommends will stop them from being installed), and suggested are purely optional and not installed by default.
You can also check in synaptic package manager (installed by default - in the administration menu I believe). Right click any package and select Properties, select the Dependencies tab and make sure the drop down is on "Dependencies". This shows you the same information that is found at packages.ubuntu.com.
As far as I know, both of those methods list the direct dependencies of the current package, but not dependencies of dependencies. I'm not 100% on this, but it would not surprise me.
if you install packages via apt-get and it is pulling in dependencies and recommended packages, before you hit the 'y' key, you can always copy the lists of packages that will be installed. Then later you can plug that list into an apt-get remove and it should get rid of all that. Just make sure nothing else you installed (that you want to keep) also depends on anything that's going to be removed.
Another useful tool is apt-get autoremove. This will remove anything that you didn't manually install (it was pulled in as a dependency or suggested package) that was a dependency of something that is no longer installed. In my experience, this doesn't always work for meta packages like kubuntu-desktop though.