Apparently Microsoft loves bignate, but not me (last 4.25 weeks of logs, not years):

# for i in 'googlebot' 'Yahoo! Slurp' 'msnbot' ; do echo -n "$i: "; cat silfreed.net-access_log* | grep -ic "$i"; donegooglebot: 19043Yahoo! Slurp: 28627msnbot: 12348