I choose to use a Mac at home, but someone pays me to use a PC every day; thus I use Outlook like everyone else in a PC-centric office...

One thing I haven't seen written yet -- the use of customized filters within the context of the inbox itself. For example, I have one set up to highlight in "green-bold" text any message sitting there that has a read receipt attached. That way I can tell if someone really wants to know that I got their message. I know some users who never send back read-receipts, but to me it is a simple courtesy to do. Also, some senders use read-receipts when they feel their message is important.

This same mechanism can be used to highlight or colorize messages based on who they are sent to (you only, a specific group, etc.) or if they contain certain terms.

I also have regular filters set up to move all mail from friends (outside my workplace) into a "Friends" folder. This way, the messages don't get mixed in with "real work" and I can allocate time specifically for responding to them vs. intermixing work & fun.