The NDA of Intel having run its course, many sites published tests of the Arrendale processors, which will certainly end up in the next ranges of portables from Apple.
To summarize the things, these new processors gain from 10% to more than 40% in performances at equal frequency with Core 2 duo while not consuming any more power. If you wish to have more details, we advise you to look at the article of Anantech, that is easy to understand and very complete.