I have a similar front-end to the Outlook Navigation demo for the panelbar using mutlipage controls, the different is they are separated by a splitter because we needed the splitter functionality.
In the solution we have we are using RenderSelectedPageOnly="true" on the multipage and using an AjaxManager so we can change the page the page when the panelbar is clicked. This was done because some of the pages called by the multipage can take a while to load and we didn't want them all loading at once.
However now each page is loaded when it is needed, which is all well and good but some of the users change page many times and others will stay on the same page.
Is there a way to have load on demand similar to the Tabstrip Demo that has the JS
function onTabSelecting(sender, args)
So once a page is loaded it is not loaded again?