I bought a 68040-based Centris 650 (http://lowendmac.com/quadra/c650.shtml) through http://ibazar.nl/ for a song. It came with MacOS 7.6.1 on it… after having played around with this for a while (keep in mind that this machine, hardware-wise, was supposed to compete with 486s) I find it VERY sad that Wintel has come as far is it has. MacOS (and even this older version) is clearly superior in every possible UI-oriented aspect. The complete system also reeks of something into which much thought has gone, unlike anything ever produced by Wintel. Well, just one of the contemporary great tragedies.
As soon as I can buy a somewhat larger SCSI hard disc for this system, it will be getting NetBSD (http://www.netbsd.org/) to think about. :)