My new job (mar 2011) provided a MBP to work on. Ever since then I've been using less and less windows. It started several years ago though
First wife got an iPod, then work started to develop an app and the boss got on an Apple kick (and we started installing
http://www.savantav.com/ on yachts). So I jumped right into a Mac Mini to program the things. However that didn't really start my push, just got me used to the OS and how to do things. Then she and I both got iPhones. That pretty much sold me and I'll never use another phone OS - Android included. Apple just does it right.
So I get handed this MBP last year and within a few minutes I'm at a terminal prompt sshing into a SunOS box that I manage - I've gotten the Java App our vendor provides up and running for provisioning, popped up iChat and started talking with the office re: orders.
On windows I would have needed to download putty, download and install another browser and then Java, downloaded at least 2 IM clients, but I know I can find one that supports everything we use.
I prefer TunnelBlick now for openVPN, I use daily Skype, Chicken, Blink Lite, and SQLDeveloper (all of which are available in Windows too in different apps). I was actually surprised by the amount of stuff available now, and by how little my workflow changed. The machine doesn't need rebooting, I don't need to log in anywhere except for websites (sharepoint mostly and our applications), and the machine build is beyond good. Gestures are awesome (I don't know why people don't like them, it makes using a trackpad very worth it.) I do have a magic mouse, and gestures on that thing keep my carpal tunnel down to a dull roar.
That being said - I'm buying my own in a month or two as a desktop replacement, and retiring my q6600/nvidia 250gts.