Recently I was working on a project to upgrade a SharePoint 2007 environment to 2010 as as part of this was working on verifying the upgrade process on a test server. When we first upgraded the content databases the Alert Me functionality was visible in the UI and working. I knew this because users started to receive notifications from the test environment. To reduce confusion the SMTP server was removed from the SharePoint configuration. This obviously stopped email being sent from the server but it turns out that SharePoint 2010 is actually smart enought to realise that it can no longer send email notifications and as a result the Alert Me functionality disappears from the UI as well. Add an SMTP server back into the farm and Alert Me functionality appears again.
SharePoint 2007 didn’t do this and I don’t recall reading or hearing anywhere that 2010 included this enhancement but it does. Nice as long as you realise it and don’t spend a whole lot of time trying to work out why Alert Me functionality is no longer available because your upgrade testers have lodged it as a defect 🙂