Ray - I manage about 1 in 4 of the Killer (I work on the original and if I screw up, I've lost - so I don't have a second try).

Look for all the 2-cell totals that are unique (3, 4, 16, 17)
Look for the 3-cells (6, 7, 23, 24) - if they're in line, it's easier.

If you can find a 9-square where the dotted lines only give one cell in the adjacent 9-square, you can fill in that cell (total of numbers less 45). This sometimes works for 2 cells outside, if they total 3, 4, 16, 17.

Then you're into normal Sudoku tactics, plus bits of other logic.

Phil