I am a casual player and don't think this would upset me as long as they gave some sort of of warning like earth trembling when he is near or your Ghost giving a warning. Sudden spawns of uber bosses on top of you are just not cool. The MMO City of Heroes had a few Uber bosses running around especially during holiday events and it didn't cause much trouble although the careless Guardian will still meet misfortune.

I am a casual (29 hunter) and would love to see some real challenge in the game - this type of event you would not have to engage in ('run away, run away - LOL). The current public events - the one exception being the MoFo on Mars that is a bear to take down - are just too easy, I can solo any of them. This type of event requires an effort of several players to even begin to have a chance at success and helps to support the game's image that 'we" are not the dominate force on each of those planets. I think the only ones it would "upset" are those that are not leveled enough to take it on, but then if they were helped by other higher level players during the event (which is kind of the intention of it being public - to have people spontaneously join together), think about how thrilling that would be for them. It is not intended to be an easy solo event, but rather to give much more credibility and challenge to the otherwise -point, shot, kill, move on events that are current.

Not this casual... I'd be thrilled

Yup, that's a possibility.