Jamie, there are many opinions, posted in other parts of this forum, that will not just disagree, but will also profess, that apple mac employees, are wrong.
That is why I made two calls and spoke to a manager called 'Paul' who went as far, as to give me a reference number, regarding this issue.
To the best of my recollection, Jamie, this is what he said:
Take it from me, your Imac will run Mountain Lion. We are merely recommending the specification required, until the final release.. The worse case scenario, will be that a couple of features may not run.
He finally concluded by saying that if if you can run Lion, then Mountain Lion will install, and stressed not to take any notice of some posts regarding this matter, and he was very ademant, about it.
I will be dissapointed and annoyed if I can't.
All the best.