I noticed that ARM binaries aren't yet provided. Does this just mean they haven't gotten around to it yet or that ARM isn't suitable for production at this time?
I'd really like to experiment with SBCL on the beaglebone. :)
ARM systems are so diverse that, unless you define a specific operating system, ABI plus floating point calling convention, and CPU type (see http://blog.alexrp.com/2014/02/18/android-hard-float-support... for a tangentially related example I found in a quick search), a binary either doesn't do you any good, or doesn't take advantage of the SIMD CPU features of your platform.
There is currently only working support for VFP hardware floating point in SBCL so the build options are reduced a bit. I think the only choice to make for a binary release would be whether to build against Debian, Ubuntu or something else.
I can't answer authoritatively, but I do know they're not really good at updating the downloads page for anything other than AMD64 Linux and the source tarball (and of course the Git repo). Usually I just build from source.
The catch, of course, is that building from source requires a pre-existing SBCL to bootstrap.
My guess is the only way to get it running on ARM right now is to get it for a non-ARM platform they have for download, bootstrap to 1.2.0, and then cross compile to ARM.
One of SBCL's claims to fame is that it doesn't necessarily require a previous copy of itself to bootstrap; it can in theory use CLISP or Clozure CL. (In practice it isn't always tested and working, and I don't know if it would work on ARM if you tried it today.)
Regarding building from source requires a pre-existing SBCL to bootstrap, it is actually true that building from source requires a pre-existing Lisp to bootstrap.