I have an old, 2008 Macbook (not Pro) 4,1. The old white plastic kind. Lion performs atrociously (at best) on it, so around half a year ago I installed Linux on it. Recently, I got around to buying a new laptop (a Lenovo), and wanted to restore OSX on the old Macbook in order to give it to family.
I figured off the bat I'd do a clean install of Mountain Lion. I have old Leopard installation media, but that's a dead upgrade path: you can't buy Snow Leopard media anymore, so you cannot upgrade it. Apple don't sell physical media for Mountain Lion either, so I went to a friend's house, logged into the Mac App store, purchased and downloaded Mountain Lion.
When I got home, the installer (which took an hour or so to image onto a USB stick) didn't work. I figured it might be balking on the HDD being Linux, so dd'd it. Nope. It turns out Mountain Lion is incompatible with my hardware.
This is where the vortex begins. I returned to my friend, and tried to get the Lion installer off the App Store (on my account), which I had previously purchased. No dice. Apple have removed Lion now that Mountain Lion is out.
I tried to install the copy of Snow Leopard my friend had. Not possible. As OEM media, it's got (very basic, admittedly) DRM onboard which restricts the installation to his hardware.
I tried to get the copy of Snow Leopard I had originally installed, when my previous employer had (kindly) purchased a stack of us personal copies alongside upgrades for work machines. Nope; they'd stopped using Macs and those were gone.
Being frustrated, I figured I'd install Leopard on the laptop and be done with it. Nope. The disc, it turns out, is scratched.
At this stage, I called Apple. I asked what I could do. I was advised I could purchase a physical copy of Lion off them, if I paid full price -- despite already having purchased it on the App Store. Frustrated, but at this stage just wanting to be rid of the device, I agreed. It turns out this was also not possible. Apple's support is in Australia, and NZ can't get the physical media (at least, I believe this to be the case; I may have conflated the issue on the phone with needing to get the media within a week).
The next day, I took the laptop to a Yoobee store (our Apple store equivalent). They told me they'd have to ship the laptop to the support centre to fix it.
So, to recap: I can't install Mountain Lion, because my hardware is too old. I can't get physical media for Snow Leopard or Lion, because Apple no longer sell it. I can't retrieve a copy of Lion from the app store and create my own, because Apple has removed it. I can't install Leopard, because my media is damaged (not Apple's fault) -- but even if I could, it's unsupported and with no physical media, there's no upgrade path. The only solution was to pay to ship the laptop off to a support centre. Ultimately, I was very lucky to find another friend on IRC who still had a Lion USB stick he'd imaged earlier, but the fact I needed to do this is... well, awful.
This is a _terrible_ customer support situation. I'll admit it's compounded by the fact I'm in New Zealand, and we have no Apple stores (fair enough: our entire population is less than several US cities), so support is harder to come by. I'll admit that, having installed Linux, I'm probably in somewhat of a minority. However, Apple's forced hardware deprecation, and removal of physical media, have made it almost literally impossible to restore a working copy of OSX on their own hardware.