I've got multiple PPC macs, but also multiple Intel macs. I only use one PPC mac with some regularity - an upgraded Cube. I think they are just the coolest looking Mac ever. I think the mini is a sad child of the Cube and the NeXT cube. I keep the other PPC macs going because they are fun to work with and 'tinker' with, and as many have said, it's low cost.
I learned how to use computers and program in basic on an Apple II+ in high school. Got to college and every thing was PC, so I spent the next 20 years using IBM, Compaq, Gateway, etc. MS Windows Vista made me consider Apple. I never cared for System 9, 8, etc. But in 2006 I got my hands on a NeXTStation and explored that. I was blown away by the fact that 1991 technology was so much more advanced that what MS Windows was doing in 2006! THAT made me consider a Mac with OS X, and I made the switch in 2007 with 10.4 on an Intel MacBook Pro. So, I came back to the Apple world with an Intel mac. However, as I learned more about the Apple 'ecosystem' over the past several years, I find the PPC macs more and more appealing. Yes, the functionality is not necessarily better than Intel Macs, but the DESIGN! I mean, the G4 line is just beautiful, especially with the consistent look from the tower, to monitor, keyboard, speakers, mouse. A lot of thought went into those designs, and under the hood they are still impressive performers, especially in the context of their time. And beyond the G4 tower, there is nothing so unique as the Cube and the G4 iMac! I'm keeping one G4 iMac just because the design is so unique. I only turn that Mac on about once a year, but I can't bring myself to 'surplus' it! For my tastes, the move to the G5 designs was a bit more utilitarian and less about the beauty of the form.
So, looking at today's lineup, it's clear the Mac Pro is still the G5 case design. I use one with a 27" monitor as my main office Mac. I love it. I also have a 2010 MBA, and love that too. Love the design AND functionality. Apple struck gold when they put SSDs in all the MBAs. However, I often wish there was a way to 'upgrade' a G4 tower/iMac/Cube to 'modern guts' so that they'd perform equal to my Intel macs. Then we'd have the perfect balance of performance and outstanding design!