Just upgraded from Microsoft Entourage X to Entourage 2004. (Entourage is the Mac counterpart of Outlook.) The most noticeable change to the interface is the three-column layout for email. The new layout is great because it's a better use of space, but perhaps more importantly, it affords an interaction improvement.
Whereas Entourage X displayed the email message list as a single, long line, 2004 shows the same info as a shorter, 2-line item. The number of clickable pixels remains the same, but instead of having to position my mouse in a target 12 pixels tall (which requires considerable hand-eye coordination), I can aim it at one 30 pixels tall. Fatter rectangles beat long, skinny ones. (Bruce Tognazzini has a nice overview of a related principle, Fitts's Law, and an excellent quiz that should be required reading for any interaction designer.)
Easier click targets allow me to focus on getting my work done instead of getting my mouse in the right target. I'll swallow hard and say it: Nice job, Microsoft. (Could it be that my potential really is your passion? Nah.)
Interesting to note: looks like 37Signals's excellent Basecamp took a slight step backwards on this issue. Prior to some January updates, on the Messages page within a project, you could click on a category by mousing over the name of the category or the space to the right of it. That is, you didn't need to mouse over the words themselves. Now you do. The benefit of the old way is, of course, bigger click areas, but also a consistent click area regardless of the length of the words. (The former implementation could have been improved by hinting at the bigger click area by adding faint rules between the links.) My guess for why they got rid of this: it stuck out like a sore thumb from how they usually handle lists of links. (Why they don't usually do this, I don't know.) Yes, I feel a little silly critiquing the gold-standard of web-application interfaces, but someone has to do it.