Have tried it and have not seen any difference. Might be "placebo" effect. I've heard the rumor before, but after trying full 50 to one side and full 50 to the other, I have seen no effect.
As a side note, on spring tuning vis a vis weight balance, I've double checked some cars, and spring tuning seems to merely approximate quoted weight balance.
For example, the SRT4 is supposed to have a 65:35 weight balance, yet spring balance has 60% of the heft over the front. The Focus RS is supposed to have a 55:45 weight balance, but the spring balance has 55% over the front. This is calculated as front / front+rear with default settings on semi-racing or racing springs. Calculating with either gives results that are consistent. I'm sure someone could come up with a more scientific calculation, though.
Maybe it takes into account the weight of fuel? I'm going to check some more. In any case, the discrepancy is very small... thus, if you're ballasting a car and want to maintain stock handling characteristics, match the balance shown by the springs.