One of my users who wasn't logged in got sql errors. After refreshing these errors disappeared. I was logged in at the time and wasn't recieving any errors. Here is what was in the error logs:
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Wed, Jan 07 2004 09:27:20 -0500 /iBASE/viewmessages.php 24.52.28.109
Unable to connect to the database! - Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

Wed, Jan 07 2004 09:27:20 -0500 /iBASE/viewmessages.php 24.52.28.109
Unable to do_query: SELECT U_TimeOffset, U_Privates,U_Username,U_Password,U_SessionId, U_StyleSheet, U_Status, U_Privates, U_FrontPage, U_Number, U_Banned FROM w3t_Users WHERE U_Number = '42' - Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

Wed, Jan 07 2004 09:27:20 -0500 /iBASE/viewmessages.php 24.52.28.109
Unable to do_query: SELECT U_Username,U_Password,U_SessionId, U_StyleSheet, U_Status, U_Privates, U_FrontPage, U_Number, U_Banned FROM w3t_Users WHERE U_Number = '42' - Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

Wed, Jan 07 2004 09:27:20 -0500 /iBASE/viewmessages.php 24.52.28.109
Unable to do_query: REPLACE INTO w3t_Online (O_Username,O_Last,O_What,O_Extra,O_Read,O_Type) VALUES ('-ANON-24.52.28.109','1073485640','viewmessages','','','a') - Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
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What do these errors mean?

The biggee is "cannot connect" - the first one. The rest are a result of not being able to connect to your DB server. Probably a momentary issue with your mysql server.