Using jQuery with Dojo?

Can someone come up with a really good reason for me not to use jQuery with Dojo?

Because the way I see it, jquery + jquery-ui is pretty fantastic, so throwing in dojo when I need something a bit more powerful (dojox.gfx anyone?) seems like it could be a good fit.

Dojo seems to keep their stuff locked tight in the "dojo" namespace, so I don't see any collisions happening, but I've given it just a glance.