I think the odds are good that there are, have been or will be planets in our enormous universe upon which intelligent life and alien civilizations exist.

Odds on communicating or visiting are a lot worse. Time is an almost insurmountable factor. You have to imagine an alien civilization technologically advanced enough to notice our existence. They will be fantastic numbers of lightyears away, and what they notice will be long over with before they can notice. Consider that when astronomers observe a supernova 'happening', the explosion has actually happened hundreds or thousands of years ago.

Physics is fantastic enough that I won't discount the wild possibility that FTL travel or teleportation a la Star Trek can be acheived. So given an alien civilization noticed earth, they'd have to have a really good reason for coming. We could imagine they are so advanced that such travel is cheap enough that they could visit just for the sake of curiousity. Certainly it's most unlikely they would make the trip for reasons of exploitation or war, because if they are that advanced, there is nothing to exploit that they couldn't find or make for themselves. There's always religion, of course - our own planet has taught us that missionaries, regardless of the state of enlightenment of their own civilization, will go out of their way to proselytize to the heathen. In fact, I'd bet on religion being the reason for any ET visit to humanity. Intergalactic Mormons!

As for reactions, I always think people are overly concerned about humans likely response to ETs hovering over London or Washington or wherever. If some idiot government did shoot at them, it isn't like our imaginary ETs with their interstellar tech wouldn't expect or be able to deal with that, or not know how nuts humans can be. And I think we sell ourselves short in thinking we would be crazed with fear or otherwise driven mad by having to acknowledge ETs existed.

(Note: I'm fighting a nasty jaw infection and taking massive antibiotic treatment along with codeine/ASA painkillers, and have noticed a slight 'otherworldliness' in my communicatin' functions today.)