Killer Sudoku

There is a new and interesting sudoku variant, the so-called "killer", in which you get no starting clues at all but you get to know the sums of certain boxes. Like this:






So far, its only available in the Times. If you want a hint on how to start, then: the sum of each 3x3 must be 45 (1+2+...9). So the middle-left box has a 36 and a 17 (sum = 53) with one box hanging out of the 3x3. Hence that one box must be an 8 (53-45). I'll leave you the rest, the guide time was 28 mins but I think thats a bit optimistic unless you're very good.