Eh, that's a false trade-off. I'm more productive on a free OS, which I can customize to my needs (since I can choose a the best window manager for me from tens of good alternatives and so on).

That's a good way to have something blow up on you once you realize that you've based everything on something with the wrong licensing, and now you're on the hook for a lot of money.

Software often has very strong lock-in effects - what you choose today may what you'll be stuck with for the next 5, 10, 20 years.

I can relate. Switching to Linux and then having a project crop up for Windows/Mac can be pretty disheartening. I suppose you can always run a VM for Windows, but it seems to be a "cheap" solution to the problem you initially decided to try and solve.

You could run the Inferno VM over OSX to use its variant of unixy commands, "os" to run OSX commands, and edit files and run commands from the tiling windows in Acme. That way you'd get the best of both worlds. This works for me in Windows and Linux (only the commands I run with "os" change, the rest of my environment is cross-platform), and I hear it works in OSX.