Well, IIP by itself has a problem with its cache - unless nobody hits on the page for the period of timeout, the cache never updates (this is because the Ca_TimeStamp is updated on each page load with the current time). If your timeout are 15 minutes - then as long as nobody goes to the page for 15 minutes, it will refresh.
The page load which reloads the cache can be pretty cumbersome; but some of the PALs appear to not cache information (like the New User PAL).
With my setup that one query was taking a long time - maybe optomization would help a little - and resulted in 30+ second load times with more than 100 users on the site.
My "workaround" for the cache seems to work okay for me - might have to increase the times from 10 to 20 minutes to help a little. Otherwise, on busy sites, you have to set your cache to 0 (which forces a new load everytime) to get updated material.
