Feel free to post them.
Hard to tell, probably less than you think. For example, many are award-winning nature photos. Photoshop or using a filter isn't allowed.
Also, most are from professional photographers. They often report whether they have modified them or not. Most aren't.
You will be surprised what light fall can do to a picture. Especially when the sun rises and sets.
To be really honest...
I think indeed that many photos here are photoshopped (to various degrees) - and ultimately, it is a matter of what you personally can accept being ok or not. My eyes do see and sense many manipulations, even the subtle ones-. And yeah, some are definitely over the top (but I personally like it, you see). I call them
"postcards"
I don't do that much in my own photography - but there is always a level of some manipulation going on, still. My personal preference is to make my images look "natural", in the sense of being acceptable to the naked eye, being perceived as natural - even if they already have diverted from how my eyes perceived reality life.
But like so many times - both analog and digital - the output of the camera is "raw" (raw material) awaiting to be formed, shaped and molded - into how the photographer perceived it, or makes it to what he wants to express. It is definitely always a transitional process, in which the photographer has influence of the final outcome.
In most real life situations for example - you often don't have such saturated colors or contrast like you see in many photos in this thread. Some turn dramatic (and more interesting) because shadows have been made deeper (darker), colors being increased, shadow/and highlights being altered.
Gradual Filter
Here is a classic tool: To make the sky darker with help of a
half gray filter. This helps to reduce the extreme contrasts between sun/clouds vs the horizon. (it is one of the most used tools for serious landscape photographers) - and it does add a lot of "aaah and oooh" in the photo; it simply get's better, more balanced, having an almost "eternal" feel in expression when done well.
Then there are certain photoshop tools, photographers tend to overuse (there is one tool that chisels out finer details making them "pop" in contrast, especially inherently weak details come out stronger. If you overdo it - yes it looks a bit artificial. You can make clouds stand as if you face a hurricane type of atmosphere... But only because you can, doesn't mean you have to.
You can see that for example in some of the cloud images. e.g. the
dying Super cell (near Spade, Texas) further up on this page... It is stronger in colors and contrast than clouds usually have.
But it still looks stunningly wonderful, and acceptable, right ?
So, while I do see many images being manipulated - I do enjoy them... with a mindset like viewing
beautiful postcards: It's like having with one leg in a paler, not as dramatic reality - and the other leg in the realm of fantasy and bright colors. Reality is beautiful, but most often in a more discrete, sophisticated way, rarely in bold ways (unless you are lucky) Photography often tends to be a bit bolder, more dramatic, colorful and empathizing.
I guess it is all a matter of taste.