Relativity is a very consistent model. Even Black Holes follow relativity, for the most part. What are the implications of this though? Personally, I believe travelling at the speed of light across the universe would not be physically possible, unless doing so in orbit of something else.
I'm not a scientist, and I can't crunch the numbers to say whether this is true or not, it's simply a hypothesis attained through logic. But it certainly is an interesting one. Think about it, if this were true, none of our calculations would have any effect. Even if we DID manage to build an engine that could send us at the speed of light, would we be able to stop it? If we did, would we even end up where we wanted to be?
Not to mention, seeing as how Time is a Relative entity, even if we did do that we could never go back to the same place again. If we did, we would potentially be thousands if not MILLIONS of years old to that point in time. Let me put it this way.
If we were to travel at 99.9% the speed of light to our closest neighboring Galaxy Andromeda from earth, it would take 50 years to reach it, as perceived by the Spacecraft traveling at 99.9% the speed of light. If they decided to send another mission back to Earth at the same speed, it would take another 50 years for the people on board to reach it. However, when they came back, 6,000,000 Years will have passed on Earth!
Now think of it this way, if we were to reach 100% the speed of light, that number would be exponentially higher. The only way for Humans to truly travel through space while staying on the same time-line would be nothing short of bending space-time itself to reach their destination.
That's why we're trying to invent Warp-Drives.