50D has better image quality than 40D. Period. If you zoom in at 100% pixel level, then yes, 40D may have better quality, however, you're then comparing 40D sensor to a 10 Mp crop of 50D sensor, not the whole 15 Mp sensor. At image level 50D produces better images, with similar or lower noise, similar or higher dynamic range, and better resolution.

If you produce a DSLR sensor with a pocket camera sensor density, you'll get 100 Mp or more on the sensor. That is already possible today, no technological problems. The problem with 100 Mp images is in the amount of data the camera would need to handle.

Any photography hobbyist should want as many pixels as one can get. There are no drawbacks (other than increased data size) in that. Signal/noise-ratio remains the same when you add more pixels, it does not go down. Small pixels do not increase noise, small sensors do. The more pixels there are, the more you can do in post processing, crop more, rotate with less visible artifacts, correct chromatic aberrations better.

The bigger the pixel density is, the better. The popular myth says otherwise, but it is false.

The reason why this myth exist is in the habit of comparing massively magnified images. The problem with this is that when you go to pixel level and compare 10 Mp sensor too 20 Mp sensor, you're basicly comparing 100% of the 10 Mp sensors light sensitive area against 50% of the other sensors light sensitive are and this does not give proper result.

Anyhow, I do agree, that 4/3 format was a serious mistake, but the micro 4/3 format instead is promising (because of camera and lens size reduction).

This is false. Increasing pixel density improves image quality and improves post processing options (CA correction, rotation, cropping). It is a common myth that increased pixel density decreases image quality. This is because people compare images at 100%. But if we have two sensors of the same physical size, one has 1 Mp, the other has 10 Mp, yes, on 100% level the 1 Mp sensor shows less noise, but we're comparing it to 1 Mp crop of the 10 Mp sensor (ie. 10% of the surface area of the sensor).

All the modern (3-4 year old or newer) DSLR's are vastly superior to film in low light. Simply the process which converts photons into information is far more efficient in modern digital cameras than in the chemical processes that film uses. If you want even better low light capability, you need a faster lens, bigger sensor or more advanced sensor technology (bayer CFA blocks plenty of light). Or a tripod ;-)

This is utter nonsense. Digital cameras are way superior to film in low light. Unless we're talking about compacts, which are close to film when it comes to low light capability.