Since I don't have a camera on my own now, I have tended to be more of a critic of some kind and be more on the lookout for the difference of how art is viewed here on Devart and also done some ratings on Photo.net (which is btw, a couple of magnitudes above Deviantart). However, there are a couple of issues I'd like to write about that me and some of my friends have been discussing.
First, PNG vs JPEG.

The preferred image format is a question of preference of taste and habit, and for many uses JPEG is fine and quite good in quality. However, I'd say that after a some considerations, PNG is a format better suited for wallpapers and pictures made from RAW's.
The reasons are:

- Extra transparency, gives better depth to the image and easier control over hues and tones.
- Better preserved image quality when stretching or scaling down the image.
- Easier to preserve graininess from cameras.
- Better bit resolution. PNG can handle 16-bit coding.

Also, PNG is more Open Source than JPEG, which makes is a bit more trustworthy.
The compression of JPEG, the formula, is some sort of Fourier-transform that is specially adapted to sunny landscape images. While that makes it good for many portraits, holiday images and such, it's not good at all for large, monochromatic images or large single colored areas.
Also JPEG has problems with showing a slight changes of hues when taking sky pictures (polarisation) or other more subtle changes in color. THe result in the more obvious cases is a sort of jagging. Usually people tend to show a picture that looks good and has no jagging, but often it's there, just that the screen usually can't cope with it (6-bit screen of somewhat bad quality 8-bit).

Those are my main points for using PNG.

The other part is of course the screen/monitor that is used to view a picture.
Not taking into account color profile's it could be said that in general most production and viewing is based on the 8-bit RGB scale. Even if that not completely true (CMYK) when it comes to the web and to the monitors we use, it's mostly true.
However. Most screens are 6-bit. Gaming flat-panel monitors, office and home use are all usually 6-bit. Laptops - usually 6-bit. Even if you calibrate it, it still only show the colors it can show, but more correcly. Also people tend to use 9300 K blue-tinted warmth index instead of 6500 K, which is more close the our sun (5300-5600 K).
If you like using 9300 K, that's fine. I like it too.
But it should be taken into account.
Now, every one are very excited about using S-IPS panels and such because they are supposedly better than everyone else along with some OLED's. But the trouble is that what panel you use is only a part of how an image on your screen will be viewed. The other part depends on illumination. There are a couple of papers here on the net that explain how backlight is done on flat panel monitors.

Also, please bear in mind that while flat panels are good, a mitsubishi/sony CRT flat glass monitor with color calibration and warm-up time of about 2 hours will be better than most of the flat panels ever can be. That's because they are analog and because their resulting color dynamic is wider.

Back to the flat panels.
Usually the backlight on flat-panels is point based direct behind the screen, either lamp or tubes lyng and illuminating the panel. However, in more engineered flat-panels, mirrors and illumination equalizing methods are used. Those of unfortunately rare, hence the usual backlight bleeding on many screens, even very expensive ones.

So, please observe what cinfiguration and environment you are working in.

B/W - best in 16-bit PNG
Very large images with oneto few dominant colors - NOT JPEG.
Images that have lot's of green, sky and sun - JPEG
And, use a good screen.