Reading a Moby Lives article this morning (fantastic blog BTW) and they posted two surveys taken by author Nathan Bransford where he asked people what they thought an ebook should cost if the hardcover retailed at $25.
He ran the first survey on June 14 2010:
And then ran the exact same survey again on February 2, 2011:
The polls are entirely unscientific but it appears that all the $9.99 pricing pushes that have been going on for the past year or two are really leaving their mark.