I use my D100 for recording nature and soundscapes, and the main difference for me over the D50 (which I also own) is the microphones. Much improved, and more similar to the D1, so I can see where dogmusic is coming from.
The D100 might be more similar in looks to the D50, and the brochure might say it's the successor to the D50 but by then the D1 had long since been discontinued. If I owned the D50 and the D1, it's the latter I would have sold when I bought the D100.
I agree wholeheartedly.
From the review of the D100 in Sound on Sound, comparing it to the D50:
"The designers ... added custom-designed electret mics that can handle higher SPLs (128dB) and have 50 percent larger capsules, matching those of their high-end D1 model
There's a better visual comparison in the photo below. Once you deduct the D1's lucious VU meters, there's not much difference in size between the three units. But you can easily see how much larger the D100's (and the D1's) mics are relative to the D50.
The D100 is a very much improved recorder over the D50 (which I own and love) in more ways than just "independent channel gain, takes SDHC cards, records DSD and PCM 24/192". The same SOS review says Sony "isolated the power supply to each circuit section, for example, and selected components specifically to reduce jitter and noise, resulting in far lower harmonic distortion figures." They also considerably upgraded the preamps and AD/DA converters, gave it 32GB internal memory, 5V plug-in-power, larger screen and a unique limiter.