I have a feeling that the prevalence of Linux on the server side has a lot to do with Mac usage amongst users in Silicon Valley.<p>A lot of the reason I switched to a Mac was because of my increasing use of Linux servers. Once our team decided we wanted off the .NET train (some time around 2003), we started looking at alternatives. At the time, shared Linux hosting was much cheaper than Windows hosting, and there were an ever-increasing number of scripts that solved common problems. The "sharing" philosophy in the Linux development community gave us greater choice and access to a lot of good (and bad) projects to learn from.<p>Interacting with Linux servers from a Windows machine is completely doable. There are tools like Putty, WinSCP, and Cygwin, that give you a local Unix-like environment on your local machine, but they always felt like a guest, not a resident.<p>Because OS X is Unix at its core, interacting with Linux servers is natural. All (nearly all) the commands and scripts that you use locally will work on your server.<p>The only remaining question is, "Why not just use Linux on the desktop." Ubuntu is great. I regularly run an Ubuntu VM on my last Windows PC. Before I sold my last PC laptop, it ran Ubuntu 9.04. I don't dislike Linux. To the contrary, it brings me a lot of the same joy that my Mac does, but there is a lot of Mac software that I like better. There are equivalents on Linux, but I like the Mac software better. That's a good enough reason to go with the Mac for me.
It's not just that "well, Silicon Valley is just weird and they all buy Apple stuff", tech enthusiasts are very likely to have Macs also due to the peer pressure. It's almost uncool to have anything else...<p>Personally I use Windows 7 and don't see myself switching unless MS does something stupid (e.g the activation that called home on each bootup).