Well, for my setup I only put the sidebars on ubbthreads - I reversed the logic so as to only include it on pages I want it on. So my $iip_call is only set to 1 in ubbthreads to include it there. With sidebars, I turned off the Summary page and have everyone load ubbthreads.php.
All my other pages are nice and snappy; just the index page was giving me problems. With 110+ users online, I'm sure I lost alot when they didnt have their page load for 30+ seconds!
I think its safe to say on any page sidebar is loaded this will be an issue.