My experiences with quad boot OSes before my RAID broken
PCBSD 7.1.1 In short I will choose being forced to use CLI (among four main BSD variant) all the time rather than using GUI desktop there. All BSD derivative is IMO still a specialty OS (Server, Router, Firewall etc) that works its best when you glued with CLI otherwise it's no match for Linux and that obviously above my head.
Ubuntu Studio 10.04 While KDE is more intuitive than Gnome, Ubuntu is so responsive. I could spent all time on it while not doing CAD jobs. Pre-emptive kernel, AMD Catalyst driver and Synaptic play important role in my experience. A decent workstation OS indeed!
Windows 7 The more time spent there I realise 7 give some valuable benefit over XP, but I will give score 5 out of 10 for compatibility and 3 for privacy. Sure I still want to play some games there.
Mac OS X 10.6.3 I like it more! When I get Quartz Extreme enabled everything changed dramatically, and once I get VoodooHDA works this will become a real deal. I also impressed by HFS+ performance (handling so much files more efficiently and faster) over NTFS. One problem, OSX's dual personality. Its console and plist editing is a hardcore feature while GUI layer offer too simplistic noob experience thus the lack of in-between tools can be frustating (for me).
Prediction: With more increasing port of industrial-strength apps (like AutoCAD, Smoke) and the flourishing hackintosh community, OSX is on the way to slaughter Windows ahead of Linux. The big problem? Apple is a platform company just like Sun with Solaris+SPARC (though Sun is dead and Solaris had been offically ported to PC) which bring tendency to a more greedy monopolist than Microsoft. While OSX virtually runs on PC hardware, Apple strictly maintain the Macintosh term consistently and how hackintosh community keep their pace also remain to be seen. The goodness? OSX's high tide popularity may also brought Linux within and when thing does get worse (monopoly etc.) Linux is there to takeover.