Much slower startup in 10.6

Before upgrading to SL, the startup process on My imac used to take 40 seconds to reach the user screen and a further 40 seconds to complete loading the desktop.
With SL (and update 10.6.1) it now takes 50 seconds plus 3-4 minutes.

I'm a relatively new mac user so I've been trying to follow suggestions in similar (but not the same) threads - including permissions and PRAM re-sets. I've also tried disconnecting USB connections on startup, but no change.

I'd be grateful for any further suggestions to try.

Did you check for any new updates for programs that you allow to start on start up?

Thanks for the suggestion, but I've just checked - I only have itunes, ituneshelper and safari that open at login - all are up-to-date.

Any further suggestions appreciated