Regarding G5's as a daily driver, I do that every day.
I've mentioned my setup in the past but I'll go over it here:
Dual Processor 2.0, 5 GB RAM, 2TB of space among four (2x250, 1x500, 1x1TB) drives. Radeon 9600XT 128MB ADC/DVI video card/Radeon 9200 128MB PCI video card. My acrylic Cinema HD display goes into the 9600XT, an HP 19 inch monitor goes into the 9200.
I run Tiger 10.4.11. My dock has 34 applications in it. Just about every single app gets use through the day or during the week. Everything I use works without fail.
Over the past several years, I haven't had the funds to buy newer Intel Macs. I picked up Gretzky in May 2013 for $100. Before then, the applications and operating system worked without fail on a G4 466, PowerBook G4 500, PowerBook G4 1.67, a G4 Dual 1.25 MDD, and a G4 Dual 1.0 MDD. But the G5 has become such a treat and rock solid (to date) that I went and set the Dual 1.25 MDD aside for a second Dual 2.0 G5, named Alison. That Mac has an exact duplicate of Gretzky's OS and application setup and does video transcoding. I am very well aware that Intel Macs would be light years faster, but the movies I make on Alison are ones that work without fail on multiple platforms.
In short, I use my G5s to do my daily business and have next to zero problems because everything I use is something I know that works. Period.
The only reason I am considering getting a newer Mac Pro tower is two-fold: I want to record widescreen HD video and be able to manage my iDevices with iOS. Otherwise, I'm perfectly happy with my G5s. If both of them died, I'd go back to the G4 MDDs. And so on and so forth until I was able to get another G5.
Is my setup perfect for today's environment? No. I'll admit that. But what I use works and I *know* it works. I'm fine with that.
I've mentioned my setup in the past but I'll go over it here:

Dual Processor 2.0, 5 GB RAM, 2TB of space among four (2x250, 1x500, 1x1TB) drives. Radeon 9600XT 128MB ADC/DVI video card/Radeon 9200 128MB PCI video card. My acrylic Cinema HD display goes into the 9600XT, an HP 19 inch monitor goes into the 9200.
I run Tiger 10.4.11. My dock has 34 applications in it. Just about every single app gets use through the day or during the week. Everything I use works without fail.
Over the past several years, I haven't had the funds to buy newer Intel Macs. I picked up Gretzky in May 2013 for $100. Before then, the applications and operating system worked without fail on a G4 466, PowerBook G4 500, PowerBook G4 1.67, a G4 Dual 1.25 MDD, and a G4 Dual 1.0 MDD. But the G5 has become such a treat and rock solid (to date) that I went and set the Dual 1.25 MDD aside for a second Dual 2.0 G5, named Alison. That Mac has an exact duplicate of Gretzky's OS and application setup and does video transcoding. I am very well aware that Intel Macs would be light years faster, but the movies I make on Alison are ones that work without fail on multiple platforms.
In short, I use my G5s to do my daily business and have next to zero problems because everything I use is something I know that works. Period.
The only reason I am considering getting a newer Mac Pro tower is two-fold: I want to record widescreen HD video and be able to manage my iDevices with iOS. Otherwise, I'm perfectly happy with my G5s. If both of them died, I'd go back to the G4 MDDs. And so on and so forth until I was able to get another G5.
Is my setup perfect for today's environment? No. I'll admit that. But what I use works and I *know* it works. I'm fine with that.