I think the best way to tackle this is to divide the post between the Republicans and Democrats. Let's start with the Republicans.
John McCainPositives: He won the most states and the most delegates. He cleaned up in the three biggest states: California, New York and Illinois. He is the front runner for the Republican nomination.
Negatives: He won only three red states last night. One of them was Arizona, where he is senator. The second was a nailbiter in Missouri over Mike Huckabee (9,000 vote margin). The only impressive red state win came in Oklahoma. This is important not only in terms of assessing McCain's appeal with The Base but also in terms of his chances of winning the nomination. Republicans (unlike Democrats) award more delegates to states that tend to vote for them. Thus, there is one delegate for every 91,335 registered voters in California and one delegate for every 60,516 voters in Alabama. So while Huckabee and Romney won smaller states, they will be better rewarded (proportionately) than McCain.
Mitt Romney:
Positives: Impressive wins in the mountains and desserts (and tundra) where Romney won every state save Arizona. Still the choice for non-southern conservatives. He still has enough money to keep fighting. He's one every state that nobody's paid attention to. See: Maine, Wyoming, Nevada, Alaska, Montana, North Dakota.
Negatives: In a word: Huckabee. Romney needed to win the states that Huckabee took on Super Tuesday. It is difficult for a candidate who is campaigning as the conservative hope to be shut out in the South. People don't pay attention to the states where he has one because, well, nobody lives there (Nevada excluded). He is apparently assessing his situation today which is polspeak for he may not be long for this race.
Mike Huckabee:
Positives: He cleaned up in the South winning Alabama, Georgia, Tennessee and Arkansas. He was handed West Virginia by the McCain people earlier in the day. If Romney decided to call it quites he might have the opportunity to go head to head with McCain.
Negatives: Outside of the South, Huckabee barely beat 20% of the vote all night. An abysmal 4% in Mass., 8% in New Jersey, 11% in New York, 12% in California. Those numbers tell me that in a head to head race with McCain he would lose and lose badly.
Republican Overview: The race is McCain's to lose. However, he is not the nominee just yet.
On to the Democrats.
Hillary Clinton:
Positives: She won California by an impressive margin. Picked up good victories in Tennessee and Arizona. Won Mass. in spite of the endorsements. Leads delegate count going out of Super Tuesday.
Negatives: Lost the majority of states yesterday. She also lost pretty badly in a bunch of states out West. She lost two to one in Georgia which was polling much closer than that. In a proportional race, losing by wide margins is a good way to lose delegates. All the pundits say the next week will be rough for the Clinton campaign.
Barack Obama:
Positives: Won the majority of states. Carried every close race of the night. Cleaned up out West by impressive margins. Apparently, has smooth sailing for the next week.
Negatives: Lost California by 10 points. Lost in Tennessee badly. Failed to capitalize in Mass. He trails in the delegate count.
Democratic Overview: I think this is the definition of a toss-up. Hillary has more delegates but it would be absurd to call her the front runner.
Overall thoughts: The AP called Missouri incorrectly on both sides (called for Clinton and Huckabee went Obama and McCain). A fairly major screw up given Florida 2000. Not enough emphasis in the media on the delegate numbers on the Democratic side. Winning states is really quite irrelevant. This is PR, it's margins that matter.