I have Canon gear and am thinking of changing to Nikon as I have heard good things about the Nikons.
Seems a very strange way to base a change of systems on, exactly what have you heard? Remember that reviewers can be as partisan as anyone, more so if there's advertising involved. There is a lot of support for Nikon from the days of film when they were undoubtably top of the pile, however in the days of digital they're still trailing behind both Canon and Sony (cue outrage).
With the D3 Nikon caught a lucky break, the headlong rush to more pixels was brought up short by the use of Nikons first sensor, a Full Frame (also Nikons first) with only 12 MP it performed well in terms of noise and thank's to the focus issues of the 1D MkIII there was a switch to Nikon. But was it because Nikon were unable to produce a highly developed sensor, because it seems unlikely that this was by design.
Canon believe that their main long term competitor is going to be Sony, who are rumoured to be about to launch a 35MP sensor (
here) There is no guarantee that Sony will continue to supply Nikon with the high end sensors in the future if and when they become established in the pro end business.
Camera technology is very much swings and roundabouts at ths time - when people start 'saying good things about Sony' will you then want to switch to them? and then maybe back to Canon again?
All of the digital cameras on the market are very capable, unless you're having real problems, or there's a lens you want thich isn't available then it's probably best to stick with the system you have, especially if you're comitted to it.