By my calculation, a loss of 30 percent of the collected light to the mirror equates to a reduction of 0.514 EV, not "approximately 0.4." The review says that is negligible, but it is half a stop. What about all this work that Sony has done to improve the light collection by detectors? I'll bet the improvement is less than 30 percent. If you want to get 30% more light collection out of a lens, you have to increase the frontal optic area by 30 %. Is that negligible? I guess it depends on who you are.
I'm buying an A99 to get improved noise performance over the A77. It will be interesting to compare it head-to-head against my A850. The question to be answered: are Sony's sensor improvements since the A850 enough to compensate for the mirror losses? Some say that modern digital technology has made noise a non factor. Those people apparently don't use sharpening, which makes noise jump off the screen.
Blorf: I'm planning to upgrade soon and I've been considering the A77 which has a similar pixel count on a smaller sensor. If it has the same number of pixels on a smaller sensor shouldn't the image come out sharper? I've never seen pixel density addressed in a review and I'd like to know how it affects image quality.
No, it will not result in a sharper picture. There are two things that determine sharpness in a raw image: lens resolution and pixel count. Having a smaller sensor means a greater demand on resolution from your lens. That said, the A77 with the f/2.8 16-50mm kit lens produces extremely sharp images. They are as good as high-end glass on a full-frame camera. I have that matchup as well as an A850 with a Zeiss 24-70. Believe it or not, the A77 with the kit lens is essentially just as good in terms of sharpness. There is more geometric distortion with the 16-50 lens, but, if you don't mind jpeg output, the A77 corrects the distortion.
Others have pointed out that smaller pixels mean more noise. That's true if all other factors are equal. I've found that my aging A850 has lower RAW noise than the A580 or the A77. The noisiest of the three is the A77. The multi-frame noise reduction feature can reduce noise by two to three stops.