>Did the same thing happen when all the forms and classes were readonly ? I could imagine that it would slow down performance if it was not because there is a lot of overhead opening tables (after all, forms and classlibraries are tables) in shared mode.

I never tried that. All the forms and classes were stored on local [unshared] drives. The forms were not opened more than once at any given time. I was able to duplicate this on my own computer. The degradation was gradual. The more times you opened and closed a form the longer it took the next time you opened the same form.