I've uploaded a /combatlog file from Onyxia Phase 1, but all the CombatLog parser I've found don't support glancing blows. I try to write a script myself to get the data but if anyone already has a parser he can download the file here:
http://rapidshare.com/files/25986524/glance.txt.html and post the results.
edit:
So I found a parser, which supports glancing blows, namely
http://www.lossendil.fr/serendipity/. According to this parser 30,25% of my white hits were glancing blow and they did 75,83% of my normal damage.
A second rogue had 24,11% glancings and they did 73,22% of his normal damage.
The difference is quite big, so we need more data input but it is obvious to see that the change isn't that good.
edit2:
The calculation of Wodahs is correct, the parser I used didn't factor in misses.