He had a simple xPages web app showing Domino webmail in one the pages, using the old, much-hated (but often used...), iframe technique.
After the Domino upgrade, the webmail was not available anymore in IE 9, unless he hit the compatibility button in IE. Who would tell all users to do that?! :-)
Before any further investigation, we had to find a quick solution:
I was wondering how to set the IE compatibility mode in one specific xPages page.
After some web surfing on the web I asked my friend to set some IE-specific meta tags in the xPage container (using the appropriate xPage properties window): the feeback was not successfull, it did not work for some reason, the iframe did not load inside the xPage container page.
After a while I found a useful web page on Julian Buss xpages wiki, about settings the IE compatibility mode using SSJS, setting some headers in the page event "beforeRenderResponse".
Here is the webpage from Julian, with tons of tips available for xPages dev (btw, I also bought the wiki iOS app!).
It simply worked (later he will investigate the problem about the upgrade).
My Italian friend offered me a beer for this quick hint, but you know, I guess I can have a better beer here in Germany :-)