I'm an Olympus fanboy from years back, having used an E-300 for ages
now.  I /love/ the dust cleaning on it, to the extent that I
considered it an absolute essential for any new dSLR I bought.  I love
the innovation that Olympus does, that leaves the other manufactures
pretending the new featuers aren't relevant (until they bring them in
to their own line and start pronouncing the virtues).  See Canon and
dust cleaning for an example of this.  I like the fact they were
willing to take a risk and create a new lens mount system that wasn't
backwards compatible with their film range to give them more freedom
in the digital domain.

For all of that, I've still changed to a Canon, becuase the ergonomics
of the 400d make it so much nicer to use (and it was the first canon
to use dust cleaning).  The buttons are more conveniently placed etc,
and on a pure usability front, 3 focal points is simply not enough.
The E-510 have almost made me regret my decision with so much packed
on the camera, and I admit I haven't tried one yet the physical
ergonomics point of view, but I can't help but note it stilll only has
3 focal points, meaning that in spite of all of its other features,
unless I want to take a photo in using manual focus, it's simply
harder to do on the Oly :\