Research I'd LIke To See

Was wondering today if any research had ever been done into how brand image affects people's online product reviews.

In other words, if you buy an iPod and hate it, are you less prone to write a negative review because you know that most people love iPods and think they're cool?

Or, on the flip side, if you own a Toyota Camry, does the flack from the whole "Saved By Zero" fiasco make you less likely to write a positive review, even if you love the car?

Not looking for educated guesses here-- it would seem obvious that some are influenced. What I'm interested in is actual research into what degree people are influenced and what percentage of them are.