Camm has been busy this summer with improvements to GNU Common Lisp. GCL is getting more efficient; on the ACL2 benchmark it's expanding its lead over the competing lisps, with more improvements coming (granted, ACL2 may be tuned for GCL, and vice versa). CONS cells have been shrunk to two words from three, reducing memory usage by 1/3, and there's a new fixnum scheme that reduce memory accesses. There are also lots of type propagation enhancements and type-driven optimizations. There's even progress on ANSI compliance, with bug fixes coming in.

GCL has this nice feature (due to the late Prof. Schelter) where it can automatically generate type proclaims for functions from type propagation on the program as a whole. GCL generates better code with proclamations, so these can really help. If you're benchmarking an application on GCL try out this feature.