|Don't ask to ask, just ask|
1. How do I uninstall modules?
uninstalling modules should give you some hints. But I personally never uninstall modules (unless there is a big problem), and I install quite a few to look at and test out. They're generally small (disk space is cheap) and generally don't conflict with each other. On the very rare occasion I do uninstall a module - I do it by hand (IIRC I've only done that once over 8+ years).
2. When I run CPAN.pm's shell for the first time, among the list of questions it asks, it wants me to tell it which mirrors to use. In North America, USA, there's about 62 url's from which to choose. Is there some option at this point to simply ask CPAN.pm to ping some of them and automatically select the quickest and least burdened ones?
Not that I know of. But geographic info is often in the mirror name for .edu's. That and you can pick quite a few and if you start having a problem it fairly easy to get back into the CPAN config.
3. Is it more common for most Perlers to just install modules by-hand and not even bother with CPAN.pm (or CPANPLUS)?
I generally install by CPAN but about 1/4 of the time tests will fail. I then revert to installing by hand to see what tests fail and if I'm concerned about them. The nice thing about this is usually, most of the dependacies are taking care of by CPAN and I just have to do the orginal module by hand. Almost all the test failures I see are on the actual module I'm trying to install and rarely the dependancies.
4. On Debian, most modules I need are usually already available via apt-get. I'm guessing it's asking for a big mess to alternately use apt-get and CPAN.pm for the same Perl installation. What do most Debian users do regarding CPAN.pm?
I can't say anything about apt-get but I do get some large/complex modules (WX modules, GTK* modules by rpm and yum. This has never caused me a problem and saved a bit of time finding external depenancies and compiling.
5. How do I keep my CPAN.pm-installed modules up-to-date? In other words, what's the equivalent of Debian's "apt-get upgrade"?
There is the upgrade command from CPAN. But be careful. You need to watch modules you heavily depend on (like DBI and your DBD's, and DBIx::Class) for interface changes. I wouldn't use any kind of automation for this /me is paranoid
6. According to the docs at perldoc.org, development of CPAN.pm is stalled and the module may eventually be replaced by CPANPLUS. However, search.cpan shows that both distributions seem to be pretty current. Will CPANPLUS still probably eventually replace CPAN.pm?
CPAN seems to be going along. I just sent a bug report and got a reply from Schwern in a day.
7. Finally, if I think I've completely botched up things using CPAN.pm, how can I wipe out everything that was installed by CPAN.pm? That is, is there a simple "rm -fr" I can do to start from scratch without touching the rest of my Perl installation?
Not that I know of, but I would doubt you could ever get to that point. CPAN makes it pretty easy. You may get into a problem with one module, but if you take your time it's pretty easy to get rid of it by hand.