Just about every week I am asked by a Nikon-shooting friend whether to switch over to Canon or not (often, this decision comes with the migration to digital). I found a good thread over at Rob Galbraith's site that you should check out, if you have the same question and are already seriously invested in Nikon glass.
If you only have a few lenses, then you effectively haven't even started collecting; you are effectively starting from scratch. ;)
Just remember that what really matters is the image you end up with, and not the equipment you use to get it. Good equipment is necessary, but for most people it just isn't going to matter what you use. An $800 Canon Digital Rebel/Nikon D70 combined with an inexpensive lens can still get you images that can easily fill a 2-page magazine spread.