Since many people ask me about these, here's a quick post about some Debian stuff:

apt-get vs. aptitude - aptitude is, IMHO, more flexible, even if you don't want to use the interective client (aptitude update && aptitude upgrade also work). If you use apt-get and aptitude now tells you that you have some unused packages, you can fix that by making an aptitude install to those packages.

apt.conf - you can configure your debian box behaviour in a really flexible way. For instance, in this box I have this:

# cat /etc/apt/apt.conf
APT::Default-Release "stable";
APT::Cache-Limit 20000000;
Apt::Get::Purge;
Aptitude::Recommends-Important "true";
Aptitude::Suggests-Important "true";