GOP - McCain seems to be comfortably leading, and has some institutional advantages. NY, AZ, CT and NJ - all of which he will presumably win - are winner take all. MA is proportional allocation, so he gets some delegates even there. While Romney remains competitive in several states, the only state where he seems guaranteed to sweep is Utah. Some of the states where McCain has a comfortable lead (at least over Romney) such as AL, GA, and IL, allocate by district. A double digit lead probably gives you all the delegates in these states. (MA is actually the only state tomorrow that allocates GOP delegates on a statewide proportional basis).
There are quite a few states where Romney remains competitive: MO, MT, probably SD (not much polling data) and maybe AK. All are fairly small. He is also competitive in CA. Allocation here is by district, and there are enough districts that the second placed candidate is sure to get a few delegates. Winning the state overall could save face for Romney, but if it is close it may not give him much of a delegate advantage.
Overall, I would expect McCain to have a 2:1 lead in number of states and more than that in delegates.
All the states on the Democrat side use either proportional or district level allocation. No-one is going to get an insurmountable delegate lead, but one candidate could easily get considerable momentum. The biggest win here is CA - especially as the next two, NY and IL, are home territory for one of the candidates. I expect Obama to romp the South (except AR) and probably win much of the MidWest. Outside the tristate area, the NE could be split. A win in CA would make him the easy favourite. Given that he is far ahead in the South, and Clinton is only far ahead in the tristate, it is easier to imagine him delivering the knockout than her. His worst case scenario gives him the South and Ilinois, which is probably enough to fight on. Her worst case gives her NY and its commuter belt - given the expecations when the campaign began, that would be fatal.