SBCL 0.9.4 has been released, and has a huge amount of changes (even more than the NEWS file suggests). One of my favourites is the compiler support for detecting attempts to modify literal data, done by Christophe:

CL-USER> (let ((a '(3 2 1)))
           (sort a #'<))
;
; caught WARNING:
;   Destructive function SORT called on constant data
;   See also:
;     The ANSI Standard, Special Operator QUOTE
;     The ANSI Standard, Section 3223
;
; compilation unit finished
;   caught 1 WARNING condition
(1 2 3)

Version 0.9.5 should be also be a good one, judging from the amount of commits approximately 6 hours since the release was tagged:

% cvs -q diff -r sbcl_0_9_4 -r HEAD | diffstat | tail -1
82 files changed, 939 insertions(+), 570 deletions(-)

(And we didn't even break Slime this time around!)