Amongst the other problems that have been mentioned, for me, the biggest problem with VSS integration was something the author alluded to in the conclusion:
"...whenever a script has been updated, the only way to reflect the changes in the source control is to script the file and update the changes".
And vice-versa - when you change your source control file, check it in you then have to remember to apply those changes to the database.
Which is why I developed an integrated source control app that automatically applies the changes to the SQL Server when a script is checked in (link in sig. small plug ). Oh, and the source control database sits on a SQL Server.
But then, as David indicated, some people shy away from the integrated editors - which I can also relate to.
So I then thought I'd throw in intelliense - only for Red-Gate to come and steal my thunder.
Karlsource control for SQL Server