I have to disagree with continuation of PPC just because the architecture is not only dead, but was also very inefficient and never got better, even in the G5. I do tech work for Mac clients and see quite a few people still hanging on to the PPC chips, but they don't cut it anymore. Anything on the web that uses flash version 8+ will cause CPU power to get anywhere from 65% to 90% just for some stupid add. Forget flash games, hulu, youtube or anything with HD content. If you're using 10.4, and don't bother with flash, then yes performance will be fine, because it was fine back in 2005 with 10.4 and a lot less intense flash/web 2.0 tricks.
Bottom line is, technology doubles practically every couple years, given that the most recent PPC computers are now at least 4 years old, that puts PPC WAY behind technology. I'm not saying that it doesn't have it's place, such as people who won't give up OS 9 (or even previous) and some of those who use really old software, 'cause it gets the job done,' but it's more worthwhile to invest in a newer intel machine. Plus anything from pre-2006 will be considered Obsolete/Vintage and won't be serviceable by Apple.
Most PC users buy a computer every 18 months. Apple's machine generally last 3-5+ years easy. But that doesn't mean the tech, or ability does.
Just my opinion.
Hate to bust your chops here, but let's go trough the list, one by one.
First: "PPC is very inefficient and never got better". Okay, let's talk efficiency. Do you know what the TDP on average for an Intel mobile chip (say Core2Duo class) is? 35 watts. Average PowerPC rating? Anywhere from 3.5 watts (my iBook 466Mhz) to around 10 watts. Also, Google comparisons of floating point operation between PowerPC and Intel chips of the same era. I'll wait.
Second: "Forget Flash games, Hulu, YouTube, anything with HD content". This is assuming that the measure of a computer is how well it handles the internet. I think most people have forgotten that a computer can do more than just be a portal to the nebulous nether-worlds. There are many ways to get YouTube on these machines other than just showing up on the site and expecting 720p content to play in the browser window. And on that topic, why do I need a high-definition video of a kid cracking his head on a half-pipe? Wasn't that already retarded in standard definition?
Third: "PPC computers are now at least 4 years old, that puts PPC WAY behind technology". Define technology. I define technology as a tool that helps accelerate work that I do that would otherwise be laborious. Judged by this definition, how is PPC "way behind"? The entire point of software and hardware development in a consumer driven society is to compel you to buy the new stuff, whether or not you actually need it. This is why Microsoft is wrestling the bear when it comes to Windows XP. That system hasn't come pre-loaded on any new computer for almost four years now, but 70% of the market is still running it, because for them, it still does everything they need it to. If Mac users were as resolute as their Windows brethren, Apple might not have been able to axe PowerPC support from Snow Leopard.
Fourth: "Anything from pre-2006 will be considered Obsolete/Vintage and won't be serviceable by Apple". Wrong again. Apple products are FULLY supported by Apple Authorized Service Centers for a full FIVE YEARS from date of build. They are then classified as "Vintage", and parts are still available for two more years. That's SEVEN years total, and only then do they get classified as Obsolete. Any tech that informs his/her customers that Apple won't support their machines within that seven year timeframe are lying hounds, and give the rest of us technicians who otherwise want to help our customers a bad name. It's one thing to suggest replacing a computer if repairs are more than what economically could be spent on a newer system, but it's another thing entirely to dismiss repair of a perfectly usable system simply because of it's age.
Fifth: "Most PC users buy a computer every 18 months. Apple's machine generally last 3-5+ years easy". So then why not use them for the full extent of their lifespan? Any technology is a poor investment, not just old computers. In fact, new machines are probably the worst thing to invest in. You will never, ever get the money back you spend on a brand new MacBook. However, the $100 I spent on my iMac G4 might come back to me if it still works in a few years and someone wants it for a collectible, and in the meantime, its been a perfectly usable computer.
Technology is only as obsolete as you make it. If everyone hung onto their computers for longer periods of time, they wouldn't become obsolete as fast because the powers that be (Apple, third parties) wouldn't have much choice but to support older machines since they represent a larger portion of their user base. That aside, if the computer is valuable to you as a tool, the investment is only as foolish as buying a computer five times more powerful than what you need in the first place.