Perspectives, Obsolete, Cost & etc
Just my humble perspectives ...
Quoting from the inbuilt OS X dictionary:
Obsolete
adjective
1 no longer produced or used; out of date See note at old .
2 Biology (of a part or characteristic of an organism) less developed than formerly or in a related species; rudimentary; vestigial.
verb
cause (a product or idea) to be or become obsolete by replacing it with something new
So based on "no longer produced", I would agree (to a certain extent) that the G5s are obsolete. The G5s are no longer produced as a whole but Apple is still apparently fixing customers' G5s. (e.g. the 'famous' leakage)
In general, the G5s are no slow coaches, no doubt not all the G5s are able to handle 1080p HD clips. Let's not forget that not all Intel are able to handle that either. More details
here.
The one thing I would like to inject into this discussion --- electrical tariffs. i.e. costs
Other factors such as the acoustics and aesthetics are pretty much debatable. But $ is a factor where most of us are concern with. From the simple outlay of cash to the operating costs, time costs etc Again, all these factors are user-determined.
And as others have pointed out, we (both users and macs) age with time. Certainly newer hardware should generally be more cost effective and no less powerful than their predecessors. That's how it usually goes. There may be some dips and spikes along the way but when one looks at the average, and to lay it out in the most simple fashion --- advancements.
So should the G5s still be used? Certainly so! Should one look towards a newer mac which isn't a G5? I personally believe so too! Snow Leopard provides an indication. If so, why am I still so caught up with my pb3400c and not my TiPB 400? My TiPB has moved on. She died earlier this year. The pb3400c is still going strong and certain not at all slow esp. when I boot up with the RAM Disk. Writing and typing in general is lovely as the powerbook is quiet as it is totally in the RAM itself. Surfing is fast, but bare minimal when you factor in the lots of flash and newer codes.
Finally, my simplistic conclusion, on level playing ground, I sway towards the fact that the G5 is obsolete. However, I will definitely get myself a G5 tower or iMac if I see one that is of both good value and pleasant to my eyes. I have much more to add above, but I think that's enough for now.
p.s. Humor me with just another short paragraph which isn't exactly related to the thread. I love the G5s. Somehow, they exude a sense of sexiness. Truth be told, the G5s are the only macs that eluded me. Such irony. That's how it has to be for now due to limited funds. Appears I've too much time on hand at the moment 
I even registered to type this out!
Last thing, I've been running my mac pro for more than 7 days with the cpu working between 90 - 95% with almost no breaks. Batch video conversions take up the major pie. Surfing, ducking (aka Adium), Joosting and more ... like what was reported by Arstechnica in Feb, it sure is tough to bring this Mac Pro to her knees! I can only wish for a faster Mac Pro simply because I feel the time taken to process all those videos are still far too long!! I happen to know that the G5s wouldn't be faster, but they sure are sexier and more appealing in that manner!
