Of course, this was a hard result to accept for most people and there have been numerous theories to try to explain how there could be multiple technic societies in the galaxy. The most interesting to me, especially in light of the rise of the web, is the "electronic mind barrier" theory. This one postulates that something like the web is an inevitable product of technological civilization. Such societies will always strive to organize their knowledge and create increasingly powerful ways to access it, giving members of the society mental prosthetics that increase their effective mental capabilities. However, such technology runs in to some fundamental physical problems, primarily light speed. The web can't really stretch much more than a few light minutes which makes it effectively planetary in scale. Leaving the web would be the equivalent of a lobotomy since any portable system could take just the tiniest sliver of the information on the web. That might discourage emigration.
This theory has another nice property. One facet of the Fermi Paradox has to do with the cost of colonization. At this time, colonizing another star system is I think possible, but would bankrupt the entire planet so it's not really feasible. However, as the world gets richer the relative cost of such an expedition will drop. This would parallel the development of sea travel in Europe in the 1400-1900 range. Initially it took crown jewels to mount an expedition across the Atlantic. Later more modest government expenditures sufficed. Still later small groups of individuals (e.g. the Pilgrims) could afford it and once that happened the colonization of the Americas was inevitable. The basis of the Fermi Paradox is that there is no reason to doubt (and many to believe) that space travel and even interstellar travel will follow the same path.
What the web inibition theory does, though, is keep the relative cost of such an expedition growing as the wealth of the society does because the acceptable amount of information to carry long grows as well. So it may stay so marginal that colonization doesn't occur or it occurs so slowly that there's no real paradox. If it takes 1,000 megayears for galactic colonization then it wouldn't be very surprising to have multiple colonization waves at the same time. There are some other issues involving Deep Time but I'll save those for another post.