Lots and lots of this in zabbix-server.log:

2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: select nextid from ids where nodeid=0 and table_name='events' and field_name='eventid'
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: select max(eventid) from events where eventid between 0 and 99999999999999
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: select max(eventid) from events where eventid between 0 and 99999999999999
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: insert into ids (nodeid,table_name,field_name,nextid) values (0,'events','eventid',0)
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: insert into ids (nodeid,table_name,field_name,nextid) values (0,'events','eventid',0)
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: update ids set nextid=nextid+1 where nodeid=0 and table_name='events' and field_name='eventid'
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: update ids set nextid=nextid+1 where nodeid=0 and table_name='events' and field_name='eventid'
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: select nextid from ids where nodeid=0 and table_name='events' and field_name='eventid'
2011-03-31 17:10:50 PDT ERROR: current transaction is aborted, commands ignored until end of transaction block
2011-03-31 17:10:50 PDT STATEMENT: select nextid from ids where nodeid=0 and table_name='events' and field_name='eventid'

Same thing shows up in the postgresql logs.

Not interfacing with the frontend does not stop these lockups from occurring.