When the server has LogSlowQueries enabled, it soemtimes logs queries that are grouped together. the separate queries are quick, it's just that the batch isn't. Here's a log of when slow was set to 100 ms:

14356:20110311:224714.804 Slow query: 0.111050 sec, "update items set lastclock=1299880030,lastns=23878415,prevvalue=lastvalue,prevorgvalue='437647537.000000',lastvalue='0.000000' where itemid=18440;
update items set lastclock=1299880032,lastns=41263491,prevvalue=lastvalue,prevorgvalue='9941915.000000',lastvalue='2420.810399' where itemid=18442;
update items set lastclock=1299880033,lastns=49000986,prevvalue=lastvalue,prevorgvalue='338113366.000000',lastvalue='0.000000' where itemid=18443;
update items set lastclock=1299880030,lastns=24895721,prevvalue=lastvalue,prevorgvalue='9936130.000000',lastvalue='1776.142108' where itemid=18445;
update items set lastclock=1299880031,lastns=46416094,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='244' where itemid=18461;
update items set lastclock=1299880033,lastns=45758819,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='0.160000' where itemid=18468;
update items set lastclock=1299880030,lastns=21584621,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='81.473287' where itemid=18470;
update items set lastclock=1299880031,lastns=47377458,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='0.131191' where itemid=18471;
update items set lastclock=1299880032,lastns=38222048,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='4.132841' where itemid=18472;
update items set lastclock=1299880033,lastns=44686547,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='14.899549' where itemid=18473;
update items set lastclock=1299880034,lastns=59769309,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='0.090216' where itemid=18474;
update items set lastclock=1299880030,lastns=22792315,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='89.068735' where itemid=18490;
update items set lastclock=1299880032,lastns=37183440,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='7090463' where itemid=18492;
update items set lastclock=1299880033,lastns=43633412,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='97.141979' where itemid=18493;
update items set lastclock=1299880030,lastns=20700152,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='16.136769' where itemid=18520;
update items set lastclock=1299880032,lastns=39990915,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='6030008320' where itemid=18522;
update items set lastclock=1299880033,lastns=47613522,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='31338119168' where itemid=18523;
update items set lastclock=1299880034,lastns=58696688,prevvalue=lastvalue,prevorgvalue=NULL,lastvalue='83.863231' where itemid=18524;
"