I upgrade when I have the money and the need.
I currently have the need - and not the cash
Neither machine we have in the house (Mac wise) will run Aperture, and i've decided it is what i want to run to catalog my pictures. I'm drowning in them.
I have a 3 year old 12" G4 iBook, 800mhz with Combo Drive. It's running, the drive has some issues reading/writing, and the trackpad should be under a recall. My Daughter is currently using it for various Homeschool stuff.
The kids have an 1.25mhz G4 eMac that is running great now. There is an intermittent USB issue, and it won't sleep - but otherwise, it's the perfect computer for the kids. I switched to running it since it has more power & RAM for photoshop.
I need something more for me, very very badly (i'm also still having to use a dying Sony R505 that is almost 6 years old - P3, for ONE application). Its just the trying to figure out how to pay for it on one income with 3 kids. Doesn't happen quick.
But i'll get there! Look at all the money I just saved "getting" FEMA to pick up fallen trees instead of having to have them removed before hurricane season.... (we had the Tornado land in our front yard - and i'm kidding, honestly i'd PAY for that to have my neighbors have homes again
)
So, when the software I need won't run on my hardware.
Tracey