If you want to do browser-based 3D rendering, WebGL looks great but simply isn’t supported in IE. Since the only other real option for browser-based 3D is to use a plugin, then it seems like Chrome Frame is a viable alternative… IE users still have to install the plugin/addon/extension but other users on FF/Chrome do not need to.
In a corporate environment we might expect installing browser-addons to be hard to get permission for… but as I say on IE you’re going to have to install some sort of plugin regardless, whether it’s generic like Chrome Frame or specific like Unity3D or your own bespoke plugin.
Does this seem reasonable, that we can simply drop IE support for this kind of specialist app and let Chrome Frame automatically run on IE when needed?
WebGL is still relatively new, and your options are not clearcut. If you are willing to wait, Flash will also support hardware accelerated 3D, but that is still in development.
There is early talk of building IE Webgl shims using Flash, which would be an alternative to Chrome Frame.
Also, depending on how intensive your 3D rendering needs are, you might be able to get away with a 3D framework like three.js, which will fall back to SVG or canvas if WebGL is not available.