Another up-shot to injecting prior to the compressor is for those people who run greater than 30 psi of boost. Above Pressure Ratios of 3:1 the air-charge is heated enough at the aluminum compressor begins to weaken from the heat.
Holset has been working on their cast Titanium compressors to solve that problem, but water injection might also help to keep the compressor wheel sufficiently cool.
Just a thought. It's probably already been discussed anyway.
Here's Holset's page on "high pressure ratio compressors":
http://www.holset.co.uk/files/2_5_1_...compressor.php
Adrian~