Core 4.4 on a Dell SC440 (upgraded to 4 GB RAM and 1TB disk) using Samba to share some storage for backup use by Windows boxes
Core 4.4 on a Dell SC440 (upgraded to 4GB RAM and 0.5 TB disk and hacked to accept a video card capable of using a 1080P monitor) my primary home desktop - X0rg-7.5, jwm, minefield7, filezilla, rdesktop, emelfm2, sylpheed, other extensions as needed. Always booted from USB stick because the same stick is used on....
Dell Dimension 4700 (a retired PC at work w/512 MB RAM and Window XP still installed on the HD) used primarily for rdesktop access to some Windows servers.
Core 4.0 on a Dell Dimension 4600 (a retired PC at work w/ 512 MD RAM and the HD and CD-ROM drives physically disconnected) booting from a dedicated USB stick, used for EDI work and as a utility web server. Openssh, bftpd, cherokee, others as needed.
Three old boxes, much like Thane's Compaq but at 350 Mhz, running... maybe tc2.x? ... it has been a while since I fired up any of them.
A Toshiba Magnia SG20 - (headless) in the midst of an upgrade to Core 4.4 (maybe 4.5, if I wait) - openssh, cherokee, bftpd, gtm5.
The first SC440 (above) will probably be getting the video card hack (like the second one) so I can retire the old 17" CRT monitor (I sometimes let the kids play online flash games on it and they're complaining about video performance - and I want to bring it back into sync (hardware-wise) with its twin).
I've switched to using grub4dos on everything, though the old Compaqs might still have the legacy grub extension.