Man, this machine still kicks ass with the early core 2 duo's. Geekbench numbers might be lower, but it feels faster. Is it just me or is it true? I find it even more responsive than an early MP 1,1.
Yeah I've got my Dual Core 2.3 running with 7Gbs of RAM and it feels just as if not more snappy than my Core 2 Duo Mini w/ 3GBs of (slightly faster) RAM.
These G5's are still work horses and there's still very useable software for them. In fact, there's even current PowerPC software being released!
Serato Scratch LIVE - Still PPC, amazing, and one of the best turntablist/DJ low-latency Digital Vinyl Systems out there, and I use it for my $1,200 Technics DJ battle setup, thus, quite nice to have a PPC version for the expensive hardware
Cinema 4D - seems to be excellent rendering software, still PPC support (IIRC)
blender - still PPC support
Lightwave - still PPC support (IIRC)
Mixxx - Still PPC support
....just to name a few
And then there's using the older versions of Apple software that still isn't that far off from current versions, like iLife '09 vs 11 etc.
And then there's the fact too that Apple still supports PPC with software and OS X Leopard updates for the OS, Safari, iTunes, and all that.