I've already said how much I love Outlook 2003, on multiple occasions. The recap: search folders, smart date grouping, notification pop-up, and the colored follow-up flags are all very good.
I think all in all, the Office team did an excellent job on the improvements That's not to say there aren't things I wish were better.
I use the flags as they are no doubt intended - to categorize the items I need to follow through with, based on what task I have to do (reply to the e-mail, call someone, read something, whatever) and/or the project it deals with. This is especially important as I'm becoming involved in many different roles in both security and development. It's hard to stay on top of everything, and these definitely help. I use categories a lot to help keep track of my action items, but these aren't as fast and useful for the quick ones as the new follow-up flag interface.
What would be awesome, however, is the ability to rename those flags. Instead of saying - Flag Status: Red Flag - I could rename the flag so I immediately know in the search folder what type of item that is and what I need to do with it.
Sure, there are other ways I can accomplish this - predefined search folders, adding criteria such as what folder they are in or what category they are tagged with - but it's not as easy as using the colored flags.