I have a MacBook Pro r3.1 and can walk into an Apple store and get support at the Genius Bar for it. I have Snow Leopard 10.6 on it, along with Ubuntu 12.04, and I can upgrade the OS to Mountain Lion if I wanted.
Which you might want, if you find that the answer you get at the Genius Bar is "OK, that's a bug we fixed in {10.7.x, 10.8.x}, that's about all the help we can offer". Yes, the Genius Bar may listen sympathetically to your problem report, but the advice they offer might be "you'll have to get a newer OS if you want that problem fixed".
I have never had anything like that happen to be at the Genius Bar. The only problem I ever had when I visited the bar, is when I got my Mac. When I ordered the Mac, online, I ordered some programs for it as well. One was a suite of utilities. Booting with the utility DVD in the drive I could run diagnostics on it, which I did. However it told me I was running the wrong version of the utility. So I made an appointment at the Genius Bar and there the tech told me I was sent an out of date disc. She suggested I contact the software company to get an updated disc. Now I didn't think that was right. Apple should have sent the right disc but since they didn't the store should have replaced it.
On the other hand I only upgraded to Snow Leopard to program in Java 6 and there was not an update available for the version of OS X I was using whereas Snow Leopard came with Java 6.
Ooh, and I don't want to upgrade to Mountain Lion because Apple is getting to be like MS. Mt Lion does not come on a DVD. Instead you have to install it by using the App Store to download it. At least Lion came on a USB Flash drive but Mt Lion does not. As I've said elsewhere I don't think I'll be buying another Apple product. I might buy another MacBook Pro but I don't think so. If I do I'll dual-boot it like I do the one I'm using now. And it's less likely I'll buy an MS Windows laptop. So for my next one I'll have to find one that comes with a Linux distro.
if you want security updates for your OS version for a long period of time, you might get more of that with Windows
As I've posted elsewhere I have a Windows NT4 PC under my desk. I bought it brand new in December 1997. In 2000 I ran Windows Update, as i usually did every two or three months, and it told me MS was not going to offer any more updates for my PC. Old updates are available for downloads, however as someone else said "Downloads != Support". Also I actually moved from MS Windows to Linux and Mac OS X because I hate MS business tactics. To me requiring Microsoft Product Activation, Windows Genuine Advantage, and other things is treating users as criminals and I hate being treated like that. Which is why I hate Apple's new download policies for upgrades.
(Oh, and I'm a Mac user, and have used OS X to work on stuff such as this [nfsv4bat.org]. Note, BTW, that, after those slides came out, we went with running a single automountd in a global session, but mounts are done by subprocesses that are, in various release-dependent ways, attached to the session that provoked the mount.)
It seems you know much more than I do about Unix and compatible OSes. I don't know much myself, but volunteering for Freegeek Twin Cities I'm slowly learning more.
Falcon