The deal breaker with Linux for me is the amount of time I have to spend to administer the thing: with every security update to the kernel I had to recompile both my wireless and VPN apps. Add to that dual monitor support sort of works if you're willing to tweak X settings (on a laptop), lack of decent APM support (again on a laptop running a 2.4 kernel), no Office (I need this for work and Open Office was a poor substitute, MS Office under Wine was unstable as a Jello mold. Then there are RPM's and dealing with dependencies (or not) when installing an app. I don't see paying $129 for an OS upgrade any different then suffering through myriad Fedora Core releases. Or worse, compiling my own kernel, taking half a day to download the latest KDE or Gnome and having to do that every 6-months or so.
What do I miss from Linux on OS X? I really can't think of much. Focus-Follows-Mouse would be nice but given the OS X menu bar, I can't think of a way to make it work though apparently one software company has along with their virtual desktop product(CodeTek). (I'm using an open virtual desktop software that I build with XCode and works remarkably like my old Solaris CDE did.
I am glad you found something that you can work with. I loaded Ubuntu onto my back up "just in case". While Ubuntu is nice, like Windows I only need to use it for an hour or two before I'm pining for OS X.