The biggest problem with PPC macs is probably the software. You have to admit when Apple was shoveling out G3 and G4 macs and advertising that they were the fastest thing ever seen, they ran like dogs compared to midrange PCs running win XP. At the end of the day, that's all that matters. For whatever reason their software stack did not do it any justice. Compare two identical PPC Macs, one running linux and one running OS X. OS X trundles along while linux flies.
Now compare two Intel macs, one with OS X and one with Linux. The performance is similar. If PPC was so great, why was Apple never able to truly take advantage of it?
Yes and no. Apple's rush to OS X was definitely a problem, as even their early G5 machines weren't all that well-suited to it - and they were putting it on mid-range G4s running at half or less the speed of even the low-end Power Mac G5! But if you put OS9 on the same machine (assuming it's early enough in the G4 cycle that they hadn't dropped support entirely,) there's a marked performance increase.
The Power Mac G4 I rescued from the recycle center (single-CPU 533MHz,) for example, is the most responsive thing I've run classic Mac OS on yet, and that includes modern computers running SheepShaver. With the exception of large webpage rendering (which would probably see a marked improvement if I had something better than the piddly 16MB video card they shipped it with,) it comes in only somewhat under my old 1.2GHz P4 laptop running XP, and absolutely thrashes my old 800MHz Celeron WinMe box.
I think the problem is less that Apple's software is
bad and more that they always insist on everyone using their latest and greatest, hardware suitability be damned. They even staged a "funeral" for OS9 when it's a perfectly workable OS (for its time) and far better suited to the hardware they were shipping when they introduced OSX.