After about 15 years on a normal keyboard (8 of those in Linux), I can safely say that it was relatively easy to adapt to the OS X keyboard. Yes it breaks muscle memory, but it's also very easy to relearn, including the key combinations for PGUP, PGDOWN, HOME, END, etc. I also recognize that using CMD instead of CTRL is easier on the hands, because I use my thumb to reach for CMD, instead of using the pinky to reach back and straining too hard. I can now use both types of keyboards with ease. The old muscle memory is still there (plus most Wine apps still need CTRL, so...).
The desktop environment definitely takes time to get used to, and there are some things which are really annoying at first, such ash CMD+TAB being application based instead of window-based (though you can add extra commands for window-based). Overall, though, after getting used to it, things really do mostly just work and integrate awesomely. It's unbelievable to be able to grab the icon of a file in a simple title bar and drop it onto my e-mail, Skype, my IDE or even a browser "upload" button. It just works. Drag and drop works amazingly well. Time-machine may use "ancient technology" but it works fucking great. I have moved whole systems in hours and retained all my files, configurations, etc. I have lost critical files and recovered them with ease. Did you just move or rename an open file? Don't worry, most apps have realized that, they don't stop working, they know you moved or renamed the file. Plus, one of the things that really pulled me into Mac was the trackpad. I love it. I augment it with BetterTouchTool and I have blazingly fast gestures for nearly everything. It really saves me loads of time. Oh, and suspend. At the time none of my machines did this transparent combination of suspend+hibernate, but I close the lid on the mac and it just suspends. It also hibernates if it notices that the battery is low, so that if it dies out, or is nearing that, it can hibernate and come back (you don't notice any of this on an SSD).
All that and it's still UNIX. I still have dozens of terminals open. I have most software that is on other *nix systems, such as Wine (wine works great!). The only real issue I've faced is that the way network interfaces work leads to some re-learning and adaptation to some new tools. However, if you are willing to spend the money, I definitely recommend the switch. I left after being tired of having so many workarounds for silly things (my last distro was....Gentoo, but I use Ubuntu and Debian before...in the days of ndiswrapper...). Gotta open Skype? Too bad it needs this special driver loaded or it'll crash pulse, so make a script for it. Want to do this? run a script. That? run a script. I had too many of these, too many small actions. I automated most of it, but I still needed to remember slight details and, over time, I have learned that it is better for me to have a good environment where I can just work and focus on my work. This is why I also buy more chargers and adapters, so I don't have the hassle of unplugging and packing a bunch of them everyday. This "philosophy" is, in great part, why I tried the switch to OSX. I'll admit at first it was challenging, but I don't really think of ever going back. Plus the hardware is great -- and the support too.
But hey, to each their own. Most of my colleagues and friends used to, like me, despise mac and complain about it. Every single one of those who tried mac have stayed there. One of them was forced to use it because of work (iOS development), complained nearly every day for months...and now he's all Mac. I just wanted to give my 2 cents :)