When printing to an SMB printer, if the credentials are incorrect then printing simply fails without notifying the user. I believe because the print job will be retried repeatedly this can also result in having a Windows AD account locked out because of too many failed logon attempts within a short interval...although I'm not sure if the default 60 second interval is enough to avoid this, I believe clicking 'print' repeatedly can trigger a lock-out. Either way, the user should probably know their credentials are incorrect.
An excerpt from my /var/log/cups/error_log:
E [15/Aug/2007:13:48:36 -0700] [Job 35] Tree connect failed (NT_STATUS_ACCESS_DENIED)
E [15/Aug/2007:13:48:36 -0700] [Job 35] No ticket cache found for userid=1000
E [15/Aug/2007:13:48:36 -0700] [Job 35] Can not get the ticket cache for justin
E [15/Aug/2007:13:48:36 -0700] [Job 35] Session setup failed: NT_STATUS_LOGON_FAILURE
E [15/Aug/2007:13:48:36 -0700] [Job 35] Tree connect failed (NT_STATUS_ACCESS_DENIED)
E [15/Aug/2007:13:48:36 -0700] [Job 35] Unable to connect to CIFS host, will retry in 60 seconds...
E [15/Aug/2007:13:48:36 -0700] PID 5834 (/usr/lib/cups/backend/smb) crashed on signal 9!
E [15/Aug/2007:13:48:36 -0700] PID 5832 (/usr/lib/cups/filter/pstops) crashed on signal 9!
E [15/Aug/2007:13:48:36 -0700] [Job 35] Session setup failed: NT_STATUS_LOGON_FAILURE
E [15/Aug/2007:13:48:36 -0700] [Job 35] No ticket cache found for userid=1000
E [15/Aug/2007:13:48:36 -0700] [Job 35] Can not get the ticket cache for justin
E [15/Aug/2007:13:48:36 -0700] [Job 35] Session setup failed: NT_STATUS_LOGON_FAILURE
E [15/Aug/2007:13:48:36 -0700] [Job 35] Tree connect failed (NT_STATUS_ACCESS_DENIED)
E [15/Aug/2007:13:48:36 -0700] [Job 35] Unable to connect to CIFS host, will retry in 60 seconds...
...
E [15/Aug/2007:13:48:38 -0700] [Job 35] Session setup failed: NT_STATUS_ACCOUNT_LOCKED_OUT
E [15/Aug/2007:13:48:38 -0700] [Job 35] No ticket cache found for userid=1000
E [15/Aug/2007:13:48:38 -0700] [Job 35] Can not get the ticket cache for justin
E [15/Aug/2007:13:48:38 -0700] [Job 35] Session setup failed: NT_STATUS_LOGON_FAILURE
E [15/Aug/2007:13:48:38 -0700] [Job 35] Tree connect failed (NT_STATUS_ACCESS_DENIED)
E [15/Aug/2007:13:48:38 -0700] [Job 35] Unable to connect to CIFS host, will retry in 60 seconds...
attaching my /var/log/ cups/error_ log