At home I have an old Apple eMac that I've upgraded as much as possible, but its days are numbered. It won't run Firefox 3.0 - I'd need to upgrade the operating system and the processor - and as a result my browser won't do a lot of the stuff I need. For example, it no longer works well with Wesabe (www.wesabe.com), which upgraded its website recently to work with the new Firefox.
Firefox 2.0 - which I had to search everywhere for after I accidentally upgraded to 3.0 without realizing it was going to be incompatible - simply does not support some of the features and plug-ins that websites are now using. In general the PowerPC G3, G4 and G5 processor line for Macs are rapidly becoming obsolete as new software is designed to work with Intel chips.
My work computer, a newer Apple iMac, is also becoming obsolete without an operating system upgrade. It's also a PowerPC G5, living on borrowed time.
I'm running Tiger at work (at home I'm still on Panther), but I need Leopard for so many things. Last week I tried to demo a free vector-based drawing program called Inkscape but the new version only works with Leopard, and older versions require the support of another piece of software that would require a massive software downgrade. I also tried to download the Safari 4.0 beta, but again that's for Leopard only. Sometime this year Apple will release Snow Leopard, the next OSX update, and I'll be a little further behind the curve. Same goes for new versions of iTunes, the new Open Office, and other third party software and plug-ins. I don't upgrade anything anymore if I want it to work.
While it pays to keep current with your operating system - or should I say it "costs?" - I'm concerned with a general approach that rewards early adopters and leaves everyone else behind. I know it would be hard for Apple to continuously upgrade software for a wide range of processors and operating systems out there, but there used to be a little more time between state-of-the-art and obsolescence. I also know that the software has to be tweaked to take advantage of upgrades in hardware, so the people who buy the newest, best-est systems can get better performance. But, really.
Unless software companies like Apple can come up with a way to upgrade software that doesn't make older versions completely obsolete I think they could stand to slow down a bit. People will spend a little bit of money and effort to keep their systems up to date, but since the hardware itself has a maximum life of about three to four years for laptops and five years for desktops you can't really blame people for being slow on the update. Why upgrade your operating system for $150 or more right now when you could put that money towards a new computer next year with the right operating system pre-installed? It's even harder to justify the expense when your core processor is on its way to obsolescence anyway. All you're doing is buying yourself a little more time.