I now rehydrate because I have found that it usually results in a shorter lag times ON MY SYSTEM. Safale has different protocols for the home brewer, printed on the 11g sachet (ie. "do not rehydrate or baby Jesus will harm a puppy!"), than on the 500g bricks that they sell to commercial brewers, which includes instructions for rehydrating.
Still, there are a lot of hazy information surrounding dry yeast. Danstar states that 1g = 5 billion cells on their packets, and THEY DO include instructions for rehydration, while, on the other hand, White and Jamil state that when they contacted dry yeast manufacturers, the consensus was around 20 billion cells by gram. Is that figure for rehydrated yeast or not ? And what about viability ? MrMalty calculates viability from production date, yet, the last tiem I looked, there was only a best by date on most dry yeast. While MrMalty says that to ge the production date, you have to substract a year to the best by date, I must come from the future because all of the dry yeast in my fridge expires somewhere in 2014...
There's also the fact that the vast majority of us do not have the equipment for precise cell counts (which are precise in the sense that they are vastly more precise approximations of the real pitch rate): we go by what calculators and formulas tell us, programs and formulas that often do not take into account many variables or who will approximate such variables (I'm looking at you slurry thickness slidebar on the MrMalty website).
All that long winded novel to tell people to take a chill pill. If sprinkling works for you fine, there is still science that proves that rehydrating is better to preserve cell viability. If rehydrating works for you and you feel it is better, fine, but be aware that you might not be pitching as much viable yeast as you think you are (rehydrating protocols are pretty precise and I'd wager a good number of us don't follow them to the letter) and that it might not make a night or day difference to only sprinkle.