For my personal mail I use Ximian Evolution as my mail client running against my IMAP server. I'm not very good at keeping my mailbox clean and typically have somewhere between 500 and 1500 messages right smack in my INBOX before I try and clean house (every month or two).
I know I could set up IMAP folders (and I do actually have around 20 folders that I move stuff to when cleaning house) and I could set up filters to have mail automatically sent to those folders. However, Evolution has this cool feature called VFolders (Virtual Folders) that I really like and allows you to look at your email in different ways.
I have around 30 or 40 VFolders set up. Most of them are just separate folders for each of my friends and important business contacts that send me a lot of mail. If I have a VFolder say listed as "Mail from Joe Shmoe" and I want to set up a rule so that all messages form "Joe Shmoe" that reside in my INBOX go to this virtual folder just right click on a message from "Joe Shmoe" in the message list and select "Create Rule From Message" on the popup menu and then "VFolder from Sender". A VFolder configuration box will pop up, make sure the folder title is set the way you want and the source of messages (I select the my INBOX on my IMAP server but it can be any local or remote folder).
If "Joe Shmoe" were to have multple email addresses (like many of my friends) then just add the other addresses by adding new "Criterion". Then any Message from "Joe Shmoe" in your INBOX will be displayed in the "Joe Shmoe" VFolder. It works much like any other filters except it doesn't actually do anything with the original messages, just an alternate way of displaying them, and you can still see them all at once in the real mail folder like normal. And you might have a VFolder that you call "Friends" that contain messages from all your friends in addition to the individual VFolders for each friend. I also get a lot of system reports from my servers. I have all of those go to a "System Reports" VFolder.
There are many different criteria for selecting a message for view in a VFolder. If you haven't played with this feature I *strongly* suggest you do. Once you use it you might wonder how you could have lived without it. You may also want to have individual *real* folders that you archive to. The VFolders already have your INBOX sorted so all you have to do is select all of the messages in the VFolder and drag them to the real folder and it will move them out of your INBOX to the real folder. I know everyone has their own techniques for keeping up with mail. I just find this way very useful for me. But then I'm not normal. :)


