Olympus Fanboy here
Call me an Olympus Fanboy if you will, I'm happy to wear the title. Salvuccim mentioned the Canon 70-200 2.8. That's a hell of a beautiful lens and I'd love to have it. But keep this in mind, it's ~$1,600 with Image Stabilization and ~$1,200 without IS.
Then consider this. The Olympus 50-200 SWD is ~$950, just as fast optically, weighs a pound less and is probably just as solid and weatherproof or at least very close.
In addition, with the E-3 you don't need to keep buying IS lenses, if that mattered, since the IS is built into the camera itself and works very well.
The Canon lens on a full frame sensor body is a 70-200mm lens. On a 40D it is the 35mm equivalent of a 112 - 320mm lens due to the 1.6x crop factor of the smaller sensor.
The sensor on the E-3 is even smaller, hence some increased noise at high ISO, but has a 2x crop factor. The 50-200 lens becomes essentially a 100 - 400mm. That's a nice sports shooting combo in a considerably lighter package than the others and at a lower cost. If tele shooting is your thing, this could be a big benefit.
As mentioned before though, the downside is you need some pretty hefty glass to achieve ultra
wide angle shots - i.e. the expensive Oly 7-14 is needed to get an ultra-wide 14mm - 28mm angle.
The 50-200 is very high quality. Here's a brief review but keep in mind this was for the pre-SWD version. The new model focuses faster and the optics are the same: http://www.popphoto.com/cameralenses...-35-ed-af.html
Here are a few shots I took with the 50-200. Maybe a little over-sharpened because I quickly rendered them from raw files just now, but the point is, its a damn sharp lens: http://s89.photobucket.com/albums/k2...eister/50-200/
Some of those were also taken with my measly old 5 megapixel E-1. And none are obviously full sized shots. In fact one shot was taken with a 1.4x extender on the 50-200. You'll never see it because the optics of the Oly 1.4x extender is also superb. The exif data will reveal which was shot with the extender, if anyone cares.
So, you throw the little 1.4x in your pocket and now you have a IS 100-400mm and an IS 140-560mm
super tele-zoom for less money and much less weight than the 70-200 IS Canon lens. Great combo? Well it very well could be, depending on your needs.
That being said, as an Olympus fanboy, I will add that I had a real hard time deciding between the E-3 and the Nikon D-300. In the end I went E-3 mainly due to it's reputation for being weatherproof and for quality construction in that price range.
Finally, the new Canon 50D looks real sweet too. Haven't read much about it but I'd love to take a good look at some point.