I've never used Mac OS X so I can't say much about it, but I have been using Ubuntu Linux and SuSE Linux for a short while. Ubuntu is very suitable for home use, and SuSE is more suitable for a business environment (which is exactly what their targets are). SuSE is quite a bit more bloated than Ubuntu and a bit more difficult to use.
I've made a switch away from most MS software a long time ago, and it's certainly much easier to switch today. Right now I'm in the final stages -- after many years of using Windows 2000, I'm in the process of switching to Ubuntu as my primary OS. You already know that you can use Firefox instead of IE, but you can also use Thunderbird or a whole bunch of other programs instead of Outlook. You should be able to export your contact list and emails to files which another mail program can import. I don't know the details though; it's been a long time since I've used Outlook.
A great alternative to MS Office is OpenOffice, initially developed by Sun Microsystems as StarOffice. The first version had some problems but the current one works very well. OpenOffice is also compatible with most (or all) MS Office documents.