The G5 is a relatively new machine and so I think it will be around for a while. Certainly that is the gamble I made when I bought mine. The Intel Macs were already out when I got my PowerMac seven months ago, but for now, and until CS3 comes out, the PowerMac is the fastest Photoshop engine available on the market, bar none. That and the other factors I talk about next decided me on the PowerMac.
Setting Photoshop aside, consider the universe of other apps out there. Even a year or so into Apple's PPC->Intel conversion, there are still lots of programs out there that are not Universal binaries. All of these run at full tilt right now on the PowerMac. No need to wait until the manufacturer gets around to releasing a Universal.
So, when you consider that the PowerMac will be viable for several more years (I guarantee that software vendors will continue to product PPC compatible versions of their stuff for a long time - a huge percentage of their addressable market is still on PPC Macs! They would be hugely restricting their possible customer base - and hence revenue - by only doing Intel versions) and the fact that by using a PowerMac, you can run ALL the available Mac apps at full tilt right now, I would recommend the PowerMac.
Yogi is right though, long term you will want an Intel Mac, but I define "long term" for this as being about three years or so. That is when you may start to see new software titles coming out only in Intel native. This will be simply a function of what percentage of the overall Macs out there are "Intellimacs" vs. PPC Macs.