Here's another thought, and really this thought maybe belongs on my blog or in the lounge, but it's relevant here.
In 2001 when the 68kMLA started (and arguably out until 2003, which was when I switched from my 840av to my TiBook) -- the point of the 68kMLA was that most of the 68k Macs were still useful for this, that or the other. Indeed, in 2003, my 840av ran a lot of the same programs I was actually using on my TiBook (word processor, QuarkXPress, PageMaker, IE and OE 4, etc.) and was able to visit most of the same websites more or less efficiently. This applies ot the last of the 68ks, which if I remember correctly is the PB190 from 1995.
Today, in 2011, it seems that G4s are in almost exactly the same boat that the 040s were in 2001-2003. You can still use them, but they are noticeably on their way out. There's not anything you can buy today, even with an atom processor, that will be slower than a G4, and while the G5 has more cores and more expandability, moving upmarket (say, to a machine with a "Pentium Dual Core" processor) will get you a machine with the same or better expansion and that *will* whip the pants off of that G5, performancewise.
If the endgame was switching to linux anyway.
So, if you want to show your solidarity for a dead platform, and prove to somebody that you can indeed use an older computer, then by all means go ahead. But if your apps are available on linux, or you can deal with Windows (and with W7, it's a lot better than it had been) and you're absolutely set on a certain budget (say, "less than $400") that can't be achieved with modern Mac hardware -- save yourself the time and heart-ache and buy a new PC and use the money you saved on upgrades/updates (outdated ram/hdd) on a backup hard disk or a stack of rewriteable DVDs for backup purposes. (or a cloud backup software subscription.)
(Sidenote: If I had to reccomend a super cheap desktop for general purpose computing to somebody today, I'd think about something with the 965 chipset or newer, and P|D or newer.
http://www.geeks.com/details.asp?invtid=OPTIPLEX-745DT-PB-3R&cat=SYS (P|D @ 3.0GHz, .5/80/XPp)
http://www.geeks.com/details.asp?invtid=223-0637&cat=SYS (Core2 @ 2.33GHz, 2/80/VistaUltimate)
That same site has cheap monitors as well:
http://www.geeks.com/details.asp?invtid=P170ST-B&cat=MON
)