Logically, it's an awfully big universe to serve as a backdrop for one small planet orbiting a middle-sized star. The number of extrasolar planets detected keeps growing as the technology improves and new methods are worked out. The basic molecules to form a possible "primordial soup" have been detected in interstellar gas clouds.
Thus, there's no solid scientific reason to think that life is unique to Earth. Considering that most people wouldn't apply the adjective "wasteful" to God, there's no religious reason to think God would have created all the rest of the universe just to keep human technicians forever employed building bigger, better telescopes.
This brings us to the next issue. If we take it as a given that there is other life out there that possesses both intelligence and technology, where are they?
Currently, SETI at Home and others are looking for radio signals. We know that radio is an effective form of distance communication, so it's within reason that this would be used by at least some technically savvy civilizations. So far, no one's caught E phoning home. There are at least 2 possible reasons for this. 1. There's no one capable of using radio in our immediate neighborhood (space is BIG). 2. Some advancement we haven't yet made will render radio obsolete, thus meaning radio signals from most civilizations will only be on the air for a limited period of time.
But them there's the problem of those who've seen something in the sky, on the ground, or even occasionally administering a thorough probing. If we believe all of these stories, that would mean that the world has already pretty much been turned into an interstellar tourist attraction and the aliens are only here to mess with our heads (Daddy, turn off the cloaking device. I want to watch those humans freak out!).
The extreme opposite point of view is that 100% of these claims can be chalked up to misidentified aircraft, other natural phenomenon, and human lunacy. A counterpoint to this is that governments are trying to hide all sorts of intriguing possibilities by means of discrediting all the witnesses. I could imagine a successful coverup of some spare chunks of crashed UFOs, but can't picture any government managing to hide direct contact with aliens or anything else really huge for very long.
In the middle ground is the possibility that at least one alien group is quietly studying us. If they wanted to initiate direct contact, there are plenty of places to land where there would be no doubts left and no way to keep it secret. If they are here, they are keeping it quiet - mostly. This would mean that there is a possibility that some of the reports are real and are due to equipment malfunctions, violations of whatever protocols they have about keeping things quiet, and other accidents. After all, it's a good idea to avoid panicking the primitives who have nukes. Think that advanced technology would render all those primitive weapons obsolete? Let a cave man get close enough to you with a club and rethink the argument.
Even is they can personally avoid getting nuked, they might not want to be responsible for the collateral damage this could lead to.
My best guess is that if we have been discovered, we're under careful observation until they decide what to do with us. So, if they are here watching us, what do they want?
If it was a simple exterminate and colonize mission, I'd assume that any civilization capable of star travel and that had studied life on multiple worlds would have the technology to engineer a plague or other disaster to remove the pesky local lifeforms who stood in the way of building some new condos. Then again, if there's a Galactic Police, there could be rules against wiping out planets like ours, so setting up something to make it seem like a real accident to other aliens investigating the crime scene might take time.
If they were here to provide us with all the benefits of their advanced science and technology, they'd have landed openly, unless they're still studying us in our "native" state to see if and when we'd qualify. Maybe we need to meet some minimum level of social or technical achievement before they'll shout "Hello" (and get dirty looks from all the expats in China who are so sick of that). It the minimum achievement is just landing a person on the next planet, we should all complain to the US Congress for screwing up plans for a Mars mission since the 1970's.
If they are checking us out as a potential food source for the future... I can't really think of an easy way to quickly discount that possibility.
Or, they're all just like me. Here to check out the amazingly hot Chinese girls.