"Viable" depends. I have a couple that I use for OS 9, and, my 7 year old, little used, Powerbook runs OS Jaguar reasonably enough to do email on, and most other computing tasks.
At a point, you just realize you can't afford Apple, or you can afford apple.
If you don't mind paying premium prices for an OS with all the nimble ability of an Old Cadillac, and don't mind selling them for peanuts compared to what you paid for them, go ahead.
Like people complain about Dells, you'll find yourself feeling screwed for the money you paid for it at one point or another.
I guess what I'm getting at is if you look at the progression of Apple software, vs. it's hardware, at least in the last three years, the software seems to eat up the hardware progress, which, is really still a long way behind PC's.
My major objection is the progress of the hardware, and software, has progressed so quickly, that it's like trying to take a freeze frame shot at a Indy car track, from point blank range. What You see is what you get, at that time, and that's all the promise is. With SCSI, the card aren't supported often times for a one year OS change, and, the component progression is similar in other areas.
Also, Apple does a lot of dirty stuff that makes components only able to be used with their OS. I have two UL2S cards that can't be flashed to PC, since they were made to Apple only specs. Funny that the card they are based on CAN be flashed. So you pay more for a card, with less flexibility.
All that said, what is it you are going to do with the machine, and how much are you going to pay for it?
OH, I forgot to mention some of the guys that bought G5's got burned, since parts, motherboards, IIRC, went out in just over a year. Now, Apple has a new, short warranty, so you HAVE to buy the three year protection.
So add that into the cost of your product.
s
PS Apple people seem somewhat dillusional about resale prices. They see
them posted, by retail stores, as proof of the value of their old products, but, I know I didn't get that kind of money for my old macs. No, there are not a lot of people that are beating the doors down to buy a Mac G3, 333mhz, for 500 dollars.
Do searches on eBay for a reality check on that one. Use advance search and sold products checked.
