Well, since I'm now officially a wonder twin (read Dan; he's a better writer and more interesting), I feel obliged to give a status report... instead of doing something useful with my time, I've been doing what might well turn out to be the most thankless port in SBCL's brief history. How many people do you know who will want to run a native-code Common Lisp compiler on the HPPA (aka "parisc") platform? Anyone?
So why, then? Well, to understand that, you need to understand a bit of history, and a bit of software engineering. The history first: CMUCL historically supported compilation on Alpha, HPPA, MIPS, RT, SPARC and x86 platforms (as well as the PowerPC, briefly); however, partly because of motivation and partly because of cmucl's build process, CMUCL currently only supports SPARC and x86. SBCL's build process is such that, in contrast to CMUCL, building binaries is trivial, so, since the backends are as good as they ever were, it is much easier for SBCL to support more platforms, particularly since we can piggyback on Debian's "buildds". Then, once all the viable CMUCL backends are ported, we can perform some much-needed surgery.