I have several email accounts, and have always liked to be overly organized with my incoming emails.  Prior to Outlook 2007, I'd create a folder under my main Inbox folder, and after setting up a new email account would create a rule to move mail coming in on a specific account to go to a specific folder.  This always worked great, but I think Microsoft actually improved things by making it a couple steps easier to accomplish the same task in Outlook 2007.

In Outlook 2007, you still need to create the folder you want your incoming mail from a specific account delivered too (you can point multiple accounts at the same folder, I choose not to), but then after setting up the account you select "Change Folder" button (if it is a POP3 email account) and select a different delivery folder. 

I think "rules" creation was probably overly complicated for the masses for this simple task, and that's why Microsoft added the functionality. Regardless, I like the new functionality.