Mac. First off, this has been my best move ever. I have always been a straddler of both worlds, completely comfortable in a PC environment as in a Mac environment. The only uneasiness I would experience would be the brief time after a switch, when I would have to get used to the slightly different shortcuts again -- Ctrl-V versus Command-V, for instance, with its different sense memory of the fingers on keyboard. Moving completely over to the Mac, however, has really opened my eyes to Mac's superiority. The Mac comes with a lot of programs that just make life in general so much easier, like Time Machine, which is a feature that makes backing up the computer so painless and easy that I never even have to think about it.
Apple Mail. This comes with the Mac, and it's worlds better than either Thunderbird or Outlook. I'd been a heavy Thunderbird user on both the Mac and the PC, but I moved to Apple Mail so that I could use some of the features of a project tracking software I bought. By far the biggest plus about Mail is the Smart Mailbox. I get a lot of e-mail, so I often file them away according to action required; e-mail I need to answer go in one folder, e-mail I need to do something about in another folder, e-mail I need to archive in yet another folder. And given that I work for a lot of different people and publishers, sometimes I need them to be filed by client as well. The Smart Mailbox allows me to filter through all of that and have just one repository for certain types of e-mail that might actually be spread out across different folders, including my Sent folder, or even across different e-mail accounts, of which I have many.
iCal. This calendar program also comes with the Mac, and I'm in love with its To Do feature. It not only shows up in Apple Mail for easy access, but I can sort them by, say, publisher -- a different calendar for each one, all viewable at the same time in color-coded goodness. I can set due dates and alarms so that it e-mails me a week before something is due, and if I want to, I can even publish my calendar online so that others can see what's on my plate and how busy I am. If you get an invitation by e-mail, you can set it up so that it automatically adds the date to your calendar.
But my true love is how these two programs -- Mail and iCal -- come together with Address Book (also included in the Mac), in a program I bought called Bento, which harmonizes all of the information in the three programs so beautifully that I now have a one-stop shop for the administrative part of my work. I'm an artist; I have the most fun doing the actual art. But now that my administrative system has been moved to the Mac and streamlined, I find that I'm starting to love keeping better track of my work, too.
So these are my new tools of the trade, and I'm still in the honeymoon phase, discovering what else I can do with these programs and exploiting the heck out of them. It makes me wonder why businesses still use the PC. Mac, despite its artsy reputation, is so wonderfully designed for business, it's a shame only artsy folk know about it.