I've currently got ~1200 actions and ~180 projects, but I've had as many as 2,500 actions and 250 projects.
As an aside, performance seems about the same for me regardless of action/project count. So either there's little impact, or a difference of ~1,300 action and ~70 projects is not enough to notice a slow down, or the threshold at which performance starts to suffer is higher than I've reached. The person we should talk to is Bill (whpalmer4); he's pushed the limits further than anyone else I know.
Anyway, perspective switching is near instantaneous for me with no sidebar items selected and about one second (or less) for perspectives with something selected in the sidebar.
Note that I have the "LeaveEmptySelectionEmpty" hidden default enabled, so when nothing is selected in the sidebar, the main content area is also left empty.
I'm satisfied with the performance of switching perspectives in the 1.8 sneaky peek, although I wouldn't complain if things were even faster. :-)
Last edited by Toadling; 2010-08-06 at 08:50 AM..
Reason: mention of Bill's HUGE database