Saw it last night and thought they did a really good job, the funniest film I've seen in a long time. There were a number of laugh out louds moments (in particular, the driving instructor scene, the bit where they stay at the jewish couple's B&B and the naked fight).
I'm glad that they avoided the Ali G route of placing in him in a fictional setting, but they also didn't overload the film with hoax interviews. It has a narrative structure that works well. It also takes an unexpected detour around halfway through and produces some tender moments that are surprisingly effective.