I don't think there's anything wrong with being curious about switching. Nikon makes fantastic cameras. If it were financially possibly I would carry both Nikons and Canons. I used a Nikon years back (the d40) and loved it. It's all about personal preference. You could be using the best, most expensive camera in the world but if its layout doesn't work with your hands you're going to hate it and take terrible pictures.
I agree with all of that.
I find that Nikons have a much better button layout, however, their camera ergonomics are lacking. Canon has great ergonomics down to a "T". For me this is important because I have tiny hands and weak wrists. Other people may not notice the difference so much. Good ergonomics is the difference between my arms getting tired and shaking, and me taking a good picture without getting exhausted in a few minutes.
This is also an interesting point - for me, where Nikon falls down is the absolutely terrible, barely readable font (aping the eight segment LCD displays of years past) and generally cluttered layout of their back LCD. On a really cheap camera like the D3000, which I have used a bit, it's nothing that prevents me from taking a good picture, and I suppose the animated graphic of the lens aperture may be useful - though I imagine many people would find it condescending and silly. I personally just found it to be a waste of space. My T1i, on the other hand, is so good at presenting data and with its button layout that I almost dread having to go to a multiple control dial layout, when I can currently do everything control-wise with my right hand. Only mode switches and the occasional unusual feature (mirror lock up) require moving a hand (in the case of MLU, it sadly requires digging into a menu, but it's still easy to find).
Nikons, as somebody else mentioned, have less megapixels in their cameras. I'm not sure if there's any data to back up Nikon having larger pixels, but generally when you raise cameras to very high megapixel counts you make the pixels smaller to cram a larger number in there. This decreases the quality of an image. I know people who would swear on whatever holy book they follow that Nikons have better coloring/image quality. I have noticed it as well, but I haven't found an unbiased side by side comparison of the two yet.
I don't want to beat the dead horse about this but this is not necessarily a point in Nikon's favor. More pixels mean that despite how good each individual Nikon pixel may look, you are getting more data points with a higher-density sensor - which is not just more resolution, but also more data for reducing noise. If you get a hot pixel on a lower-density sensor, you stand to lose more details.
There have been some heated debates on DPR Forums about the suitability of using some units for discussing pixel density over others. Some have pointed out that "pixel density" is a derived unit, and thus harder to gain insight from, when pixel pitch is a perfectly suitable measurement.
It does seem plausible to me that there are some improvements in ISO sensitivity possible with larger pixels - after all Nikon cameras seem to have achieved this - and of course we don't live in a world where throwing more pixels at a problem makes it go away; ISO-centered cameras are still important. But, barring ISO critical photography (and even there, much of the time), if you had a binary choice between improving lowering noise or increasing resolution (which seems a false, oversimplified binary choice), for now increasing resolution gives benefits for noise as well.
One final random note: For a while I took it as gospel that Nikon's use of Sony sensors meant that Canon was in a much better position for the future as it did sensor development in-house. But lately some reading about new Sony sensors has led me to wonder if the old paradigm is not assured and that Sony, with the current "also ran" status of the Alpha series, will enter the top tier with newer cameras. Their line seems to be lacking in some important areas (lenses, marketing, website details, possibly more but I can't comment on service etc. having not used it) but I would not count this big (biggest) developer of DSLR camera sensors out yet. From Canon's point, I wonder if they will be able to match some of the developments Sony has made to stay competitive.