It's hard to tell as at the same time of purchasing I upgraded to Lion, but I went from being able to code in a coffee shop for around 4 hours with the 2010 MBA

It's hard to tell as at the same time of purchasing I upgraded to Lion, but I went from being able to code in a coffee shop for around 4 hours with the 2010 MBA to around 2.5 hours with the new i7 MBA 11.