The exchange with impassioned author Robert Hastings under my earlier post "UFOs and Nukes: No Truth is Out There" made me think about the whole interstellar problem again.
I was once on a study for NASA where we read the literature and talked to some of the top people on exotic propulsion ideas. As much as I want it to be different, faster than light (FTL) travel for solid matter like a spaceship is centuries off, if it's solvable at all. It may not be. The ideas involving the most powerful systems we can think, of, using antimatter, don't get you anywhere close: as you near lightspeed, the energy requirements approach infinity.
An alien civilization may, of course, well be a thousand years ahead of us, but the laws of physics will still apply. I do think there are civilizations out there, but the extraordinary claim that at least one is visiting us requires extraordinary proof, and the burden of proof is on those aruing that extraordinay claim. No collection of anecdotes and radar anomalies, however sincere and intriguing, gets me to the "spaceship" conclusion. The FTL problem makes it entirely reasonable to demand an actual spaceship.
It seems likely that a sufficiently advanced civilization will be able to send information FTL using entanglement ("spooky action at a distance"), but spaceships? That's a very big unknown.