I was listening to a talk on The Singularity, and it occurred to me that that might be a good explanation of the Fermi Paradox. (Which is similar to the author's idea, but a bit different.) Basically, our minds are likely to "merge" with the Internet, allowing us to tap into the internet as our personal and cultural memory storage system. But we cannot extend Internet access into outer space, due to latency and the inability to make copies of the entire Internet locally. So the future "us" would be tied to the planet in order to have access to our memories, which would be very difficult for us to live without.
If you want to follow that thought through, the future us would probably like higher fidelity of their memories and recordings, approaching real life quality. The limiting factor in doing this is likely the energy consumption (and in many other ways as well).
The cheapest energy source by far is the Sun, consequently we will need to build Dyson spheres, thus pushing us off the Earth. Once we are at that stage the only way to get more energy (to support further fidelity or population growth) will be the other stars and similar mass concentrations, which will eventually lead to colonization of the galaxy and beyond to galaxy clusters/super clusters. Even the light speed barrier can't prevent such a movement for too long.
A Singularity will likely only hasten the process (there will be nothing else to do).
