seeing double-slashes in paths after 3.1->4.0 upgrade

[jonathan]

I'm seeing lots of broken (404) links after a 3.1 to 4.0 upgrade.  The 
system seems to be generating lots of urls of the form: 
http://site.com/roller//path/to/page (a double-slash after the webapp 
directory).

I'm sure I have a trailing slash set up somewhere I shouldn't, but I 
can't find it.  Some insight into where I should be looking?

thanks.