I have server running mysql and when I do a 'show processlist' at a mysql command prompt, I see a lot of INSERT and UPDATE queries from one particular user with a state of "locked" and very high times--some as high as 700 seconds. Could someone help me to understand what is going on here?
Something tells me you are using a bunch of MyISAM tables.
Keep in mind the MyISAM tables perform table-level locks when doing any DML (INSERTs, UPDATEs, DELETEs). Such statements block other like statements. Even SELECTs can block DML.
If you convert all the MyISAM tables to InnoDB, this problem should disappear because InnoDB does row-level locking thus allowing rows to be added, deleted, updated and selected without lock contention.
CAVEAT: If any of the MyISAM table have FULLTEXT indexes, such tables cannot be converted to InnoDB. For all other tables, please convert them to InnoDB ASAP !!!