So far most (if not all) of the extra-solar planets discovered have been giant beasts in remarkably bizzare orbits around their suns. Would it even be possible for such solar systems to host earth-like planets? According to research done at the Open University in Milton Keynes* it is quite possible.
By creating a mathematical model of a representative solar system identical to one discovered so far, and then "rolling" earth-like planets around in it, scientists Barrie Jones, Nick Sleep, and David Underwood found that the giant planet contained within created "disaster zones" around it. These zones represented areas in which any sort of earth-like planet would either get bounced out of the solar system or get pulled into the giant planet or the star itself.
However, planets outside these zones tended to inhabit "safe havens" that would allow stable orbits for long enough periods of time that life could evolve. If a safe haven coincided with a solar system's "habitable zone" (where temperatures should allow liquid water to exist), then it should at least be possible for a solar system like this to contain at least one earth-like planet capable of supporting life.
Once they ran their models against the 160-odd solar systems in which planets are known to reside, they got a surprising result... fully half seem to be capable of containing a habitable planet.
Now, this is not the same thing as finding another blue marble out there, but it should help by indicating which solar systems we should focus our attention on, and which we can safely ignore. Ain't science grand?