I've used Nikons all my life, and I'd say Canon have the edge.
Their lenses are that little bit sharper from what I understand, and their bodies seem to be that little bit ahead with Nikon catching up.
I don't think it is as clear as that.
Some lenses the Canon equivalents is better, others the Nikon. Canon update their lenses more often though, and are usually a bit cheaper. Nikon don't have F/4 pro zooms, but Canon doesn't have the 14-24 2.8 or 200-400 4.0 which are astounding lenses. In general Nikon does wide angle stuff better, Canon make more primes with more frequent updates The Canon 17-55 IS EF-S is great relative to the Nikon 17-55, but the Nikon 24-70 2.8 is much better than the Canon.
Horses for courses.
As for bodies, Nikon I think is well ahead at the moment, especially in terms of features and ergonomics. For sometime Nikon lagged behind in the sensor design but since the D3/D300 debut Nikon has had the edge really. No sign of that changing, the Nikon D5000 sensor seems to be the best in its class. But it is hard to compare, Canon don't have a 24MP pro body, they don't have a pro level DX body like the D300 and they don't have a low noise sensor like the D700/D3 cameras. The D700 is streaks ahead d the 5dmk2 in most ways but ultimately they do different things better, e.g.. the 5dmk2 is great for landscapes but poor for sports, the D700 is excellent for sports and great for landscapes but giving less resolution.
The bottom line is the Canon ergonomics are not their selling point. When I went to purchase my first DSLR I was intent on the Canon, but the Nikon equivalent blew the Canon out of the water. Since then every Canon I have used apart from the 1D range has really sucked in handling. Specially the 350-500D type cameras, really awkward. But thats me. This is just something that Nikon is better at.
IIf you have a strong preference for landscape work, Nikons line up is best (14-24...) IF you prefer primes then Canon is best If you want exotic telephoto lenses the Canons are much cheaper.