I have a PowerPC G5 circa 2004/5
It's still a workhorse and with Leopard and some new RAM I recently added it runs better then the day I bought it... it even still holds it's own against newer machines I work with.. while it might be slower and a bit more cumbersome in places, I've integrated it into many Final Cut Pro workflows when I just need a machine to crunch on some video compressions or need to loan it out to a client.
For the most part, I do all of my work primarily on my new MacBookPro (1 year old) and on my client's editing systems. I'm holding on to Final Cut Studio 2 for the moment, but as my clients upgrade, it's apparent that I'll have to follow suit pretty soon. Since my G5 only supports FCS2, it's going to make things more complicated when I want to use it in workflows... yes, there are work-arounds, but you can only add so many hoops to jump through before an additional tool like this just becomes impractical.
To be honest, I never expected this thing to be relevant for so long... having grown up on PCs, I expect a computer with heavy use to last little longer then 2 years before I have to replace/overhaul it completely... it's just a shame that here's this fantastic machine that's fully capable of doing some heavy lifting, yet due to a handful of conflicting software versions it's sort of become the basic 'home computer' rather then the loyal stallion it once was.