Currently, I have two machines at work on the go. One (koala) is building the 2.4.21 kernel. The other (starfish) is compiling up its new Gentoo distribution. There's also a machine at home (newuk) which is a Sun Ultra 10, currently rebuilding its entire collection of programs, because I think I managed to compile some for the wrong architecture in a cross-compiling experiment which failed.
The cunning plan is that starfish, although a fairly weeny dual P2 machine, is going to be a test bed for user mode-linux. Because of 'historical issues' at work, all the websites that we do have UNIX paths hardcoded into their PHP, such that they all have to live as subdirectories of a given folder. Also, some are PHP2 (sad but true), and some are PHP4. This makes developing a bit of a hassle. We recently figured out that storing sites in CVS was a good idea, but unfortunately everyone shares the same check-out sandbox which ain't ideal. The plan is that if each developer had their own Linux machine, they could each have their own checkout area.
So far, so good, except that this would appear to call for twice the number of development machines as we have at present, and then they'll all need keeping up to date with the same versions of Apache, PHP etc. But, with user-mode linux, hopefully each developer can have their own virtual machine. And each virtual machine will mount the partition containing the relevant programs over NFS, and so the actual disc images ought to be fairly small.
This has the additional bonus that we then have two gentoo machines, and I can persuade them both to use distcc for compilation.
For my next trick, I intent to figure out how to build an Intel to Sparc cross-compiler on my ix86 machines at home, thus allowing me to compile stuff on my Sun box reasonably quickly. And then, I shall turn my attention to the Sun IPX box sitting on my bedroom floor, which is being obstinate. Hopefully, I can use the Ultra 10 to compile up all of its software, get it on there somehow (NFS?) and have 5 Gentoo linux boxes to play with