Red Carpet has a nice package abstraction layer that allows us to support RPMs and DEBs transparently.
There are a lot of people who've been able to ditch their Windows machines and switch over to Linux because they can now use their Exchange server for calendaring and collaboration from their Linux desktop.
We plan to support Exchange 2003 as soon as it is released. We already have the prerelease versions from MSDN.
GNOME is aiming for simplicity and consistency; we're the first open source desktop project to have a documented set of human interface guidelines.
I'm personally working on converting about 250,000 different Windows machines to Linux desktops, primarily in European government.
I started hacking in Mono a few months ago for some personal projects, and was very impressed with how complete and usable it is.
There's a lot still to do in Evolution.