In reference to the Kepler 22b news:
The Kepler team had to wait for three passes of the planet before upping its status from "candidate" to "confirmed".
This is possible because the planet has a orbital period ('year') of 289 days, and so it has transitioned more than once (as above) since the Kepler mission started.
However I've seem some confirmed exoplanets that have orbital periods in 10s and 100s of years, and therefore could only have been detected once by Kepler.
As far as I'm aware all methods of discovering exoplanets require the planet to pass in from of their parent star (i.e. we can't use a telescope to 'zoom in' and see them directly)?
So how are exoplanets confirmed, when we haven't been searching long enough to cross in front of their parent star? How long does the transition even last?