Hello,
Juho Snellman recently[1] posted a very useful SBCL-specific coverage tool. I did this for CFFI to test the coverage of cffi-tests. The report can be found here:
http://common-lisp.net/~loliveira/tmp/cffi-tests-coverage/
The results seem pretty good to me: 80.5% code coverage. It does reveal some missed spots so if someone feels like writing some tests, look at this report for picking where to start. :-)
A significant percentage of these missed spots are a result of compiler macros (or type expansions) kicking in or error branches not being exercised.
[1] http://thread.gmane.org/gmane.lisp.steel-bank.devel/8721