Going into the debate, Biden seemed like the underdog. He has a long history of saying strange things. Surprisingly, he did great. He was everything that Obama was not. He was animated and belligerent. As the debate continued he allowed Ryan less and less time to talk. He stole a page from Sarah Palin's book. When asked a tough question like Libya, he went off on a different subject, refusing to answer the actual question.
Biden also lied with ease. At one point he managed to tell two lies in one statement - he asserted that the economic crash was caused by Bush's Medicare Drug Benefit and two unfunded wars and that he voted against them. These had nothing to do with the crash and he voted for both wars and was a supporter of the drug benefit up to the final vote.
This is not to say that Biden's performance was perfect. He forgot to practice his expression. At times he looked angry like he was about to attack Ryan, possibly biting him. Other times he smiled or even laughed at inappropriate times. He was probably reacting to Ryan making statements that Biden had rehearsed answers to but it came across as strange. This may be the main thing that people remember from the debate.
Ryan did a decent job when he was able to speak without being interrupted. He didn't make any mistakes and he pushed the party line.
The moderating was terrible. At different points the moderator started arguing with the candidates. She also never made an attempt to stop Biden's constant interruptions.
If these guys were at the top of the ticket I would be worried. Instead, Obama is at the top and it just isn't in him to act this way. He likes to speak in a professorial voice. He is not a street brawler.
One thing that will help Romney in the long run: Biden telegraphed the attacks that Obama will use. This gives Romney time to rehearse defenses against them.