I am an anal SOB. I detest oxidation. I have always followed the rule of thumb (as Denny stated) as 80F or below before I start moving the wort rapidly to chill it faster with my crappy IC.
For those of you not worrying about this, have you observed any ill effects (HSA potential) from long term aging of beers? For example, if one is rapidly stirring wort at 185F for a hop stand, I am assuming that the massive hop flavors/aromas combined with consuming the beer rather quickly (as IPA's usually are) would help to mask any initial oxidation potentially contributed from HSA (if any at all occur). Just curious about aging beer with regards to this, as I (and many others) were curious with Brulosophers Exbeeriment on this topic as well.