Hi, first of all i'm a nikon user, just share a bit why i chose nikon at the first place, and what's the pros and cons that i found when using the system.
First, when I first bought the D90, it's the only camera that fits my hand best (500D was too small, 50D was too big, 60D was not born yet). Besides, Nikon offer better entry level system at that time. Meaning the entry level lenses is more attractive there (e.g. 18-70, 18-135, 18-105 VR, 16-85, 18-200) which canon do not have at that time. And primes that i like are all available in Nikon line up. And I did not and still don't want to spend too much of my hard earn money on camera stuff. Overall i'm quite happy with it. Eventhough canon had come out with similar offering, but price is much more expensive (i'm talking about entry lenses).
Here's come with the cons, if you intend to upgrade your lenses, there is less bridge between the entry and pro lenses. Either you stick with quite good entry or u folk out big money to buy those 2.8 lenses. For Canon, there is f4 offering which is more affordable.
After all, its depends which brand that makes you feel more comfortable, as long as you happy with it, it's a good system.
Best idea is to stay with what you have now, but if you feel happier to jump ship, then do it sooner rather then later, since you are still new (i assume) and have little lost if sell your current setup.
Cheers.