slime has been updated to 2.0_p20081209 in the gentoo lisp overlay, but it cannot be installed because the file slime-2.0_p20081209.tar.bz2 is not available on any mirror. Reproducible: Always
Right, the Gentoo mirror system does not do anything for overlays. For overlays, the SRC_URI needs to be correct. Assigning to maintainers for fixing. (I think common-lisp is correct, I don't see anything in layman -L for lisp)
Oops, sorry for this. I had uploaded the tarball to common-lisp.net but forgot to update SRC_URI. It's fixed now.