We use ChromeFrame extensively with IE8. The reasons are varied for why we are still on IE8, but we found that it was much more complex to "lock down" Firefox (I seem to recall Fiefox developers advising that Firefox isn't for enterprise/lock down) & Chrome, also our MIS system only supports IE7, 8 & 9. As we still have a large number of XP computers IE8 is our only option.
*but* Chrome is now much less complex to control via GPO (in a similar vein as IEs) and google have now introduced a sort of "reverse" ChromeFrame, (with ChromeFrame you can decided what will be the default render, but also force sites to use IE or ChromeFrame) where Chrome is the default, but you can force certain sites to render in a different browser.
Using Chrome as the standard though, brings a number of other problems, not least the fast update cycle of Chrome, which if we allowed automatic updates means that we have 1000 computers trying to update from the internet when they turn on, and likely find no one can access the internet due to a faulty update ...
(In the same way we don't have individual computer going to windows update, we use an internal WSUS server, Chrome needs somthing similar, a repository we can point to that is local)