There are upgrade paths for them:
1. RAM.
2. Hard drive.
3. USB. Hard drives (not bootable), scanners, musical equipment, digital still camera, compressed video camcorders, printers, modems, fax machines, MIDI equipment.
4. Firewire. Hard drives, scanners, musical equipment, video camcorders compressed and uncompressed, file sharing with other Macs, target disk mode with other Macs, Migration Assistant with other PowerPC Macs.
5. Ethernet. Network hard drives, routers, modems.
6. WiFi 802.11b and 802.11g for wireless networking to AppleTVs, Apple Airport base stations, and numerous third party wireless routers.
7. Mini-Toslink. Digital audio 5.1 speakers systems, and multichannel digital audio input.
And that's just the iMac G5. PowerMac G5s have variety of PCI cards which can offer fiberoptic networking, extra SATA hard drives, and better graphics card support.
About the only thing you can't do with an iMac G5 and PowerMac G5s are native Windows support, and a few modern software packages, but most have older software counterparts. The question becomes what do you want to do with your computer? Is there a software out there that does what you need? If there is, there is no reason to let it sit and collect dust.
Message was edited by: a brody