I think the thing that makes Olympus tempting is their lenses. The Nikon kit lenses may be about as good, if you count the Nikon 55-200 f4-5.6 vs the Zukio 40-150 f3.5-4.5. But when you look at the next step up, the Olympus zooms look really good.
The 14-54 f2.8-3.5, which was the kit lens for their pro series, is a nice step up from the Nikon 18-70 f3.5-4.5(with a similar effective range), for only about $100 more. And they have a 55-200mm for about $850 that ranks with the best lense made in the photozone user survey. With a 400mm reach in 35mm equivalent, I think you might have to pay 2-3x as much in Canon or Nikon glass to match it.
Where I think they're lacking is in enough good prime offerings. There are a couple of good affordable Sigma f2.8 primes, a 105mm and a 150mm-two of Sigma's better offerings. These are available in other mounts--though with the 2x crop factor they give effective ranges of 210mm and 300mm on the Olympus. But there still aren't quite enough low to mid priced primes available in wide to short-tele focal lengths.
But I think for a shooting style that leans toward more telephoto, the Olympus system is very attractive. On the wide telephoto end, they get a bit more expensive if you want to go beyond 28mm equivalent (and there are only a few lens oprtions to do so). It sounds as though performance is more average (including autofocus), and where that's a major issue, maybe Canon or Nikon might be better. But for features, the Olympus cameras are very competive.
Some good lens review links: