Are your alerts not sending email? Use these stsadm commands to verify your alert settings.
I recently had a colleague asking me to troubleshoot some workflows. Apparently the workflow should send emails, but nothing was coming thru.
As part of my troubleshooting I came across 2 stsadm commands that may help you identify an issue with your alerts.
Although these commands did not help me solve the issue (a reboot of the Frontend did 
), I found these commands worth writing down in a post:
First command:
stsadm.exe -o getproperty -url <http://problemsite> -pn alerts-enabled
this command should return: <Property Exist="Yes" Value="yes" /> which means that alerts are good on the site
Second Command:
stsadm.exe -o getproperty -url <<http://ProblemSite>> -pn job-immediate-alerts.
this command shoud return: <Property Exist="Yes" Value="every 5 minutes between 0 and 59" />
What else can you do to troubleshoot?
Open the MOSS Central Administration page, click Operations--Timer Job Status,
make sure the following two jobs are showing "success" and 100%
Change Log
Immediate Alerts