The very fact that Earth is inhabited by humans, not some alien colonizers that settled a billion years ago, could mean a few possibilities:
-We ARE, in fact, alone
-It is impossible to circumvent, in any way, the limitation of light speed
-Life capable of traveling from their own planet is exceedingly rare
-Earth an alien experiment, or a sort of 'wildlife preserve' protected by alien powers (as in the nifty freeware game, Transcendence)
A Star Trek/Wars type of universe with an abundance of alien species is extremely unlikely. I hope it is just that intelligent life is very, very rare and not that we're permanently stuck here in this solar system.