Ian,
This is good conversation and I agree with you, I am not selling any particular tool or browser either. Just trying to be informative, as you are, as to what's out there and how it compares.
I agree with you 100% on the browser updates, FF users are much better informed when an update is available. With IE, it relies on the Windows Update feature and many users don't have the automatic updates turned-on.
We went through quite a few different HTML editors before settling upon one. We even tried FCK and had issues on the MAC platform with it as well. We ended up sticking with the HTML editor from Telerik and have been pretty pleased with its cross-platform functionality.
That's not to say that we didn't have some minor issues along the way, but they were issues that we were either able to solve or ones that Telerik addressed once notified and confirmed by them.
With that said, our only suggestions to users of our custom portal framework are advised that the only supported browsers for the MAC are FF and Safari.
What we've done is to set a base (in the DB) of what the browsers and versions are that we support. From there, schools are allowed to select (in there settings) which of those browsers they want users to be able to use. If a user comes into the portal using a browser that is not supported, they get a nicely formatted page with the supported browsers listed and links to download them.
I would go even further and suggest that this type of functionality should be in the core of DNN and accessed through Site Settings.