Like John, I can't really speak for pros either. I think it really depends on the person, as some people like to do post-processing, and others are real sticklers about doing everything in camera, with minimal (if any) post processing. 

A couple landscape photographers I like span the range. [Joseph Holmes][1] is a great photographer who doesn't seem to do much in the way of post processing. A lot of his work is film, but is more recent stuff is digital. All of it looks pretty much the same (an amazing feat in and of itself to keep your digital work and film work similar.)

[Mark Adamas][2] is widely considered one of the greatest landscape photographers of our time. It is quite clear from his work that he does some fairly ample post processing of his images, which these days are all digital. His work is excellent, and particularly saturated and vibrant. Some of his works are compositions of a few shots (such as his image of a high mountain river with the milky way in the background.

In my own work, I've gone through a couple phases. For about 6-8 months after I first started photography, I did some pretty heavy post processing. I would spend hours fine tuning each pick, even more hours trying to use HDR to create "better" photographs, etc. My tactics have changed entirely in my more recent work. I have switched to putting more time into each shot, making sure I am using the correct lens (often taking the same shot with a variety of lenses and focal lengths), making sure I have exactly the correct exposure (resorting to graduated ND filtration rather than HDR when a scene escapes the bounds of my cameras dynamic range), using live view and treating my camera like a large-format view camera to get precise composition and perfect focus, etc. My latest work requires FAR less post processing, and is notably better than my early work where I relied more heavily on post processing. Where I could spend days working an HDR image and its tone mapping to get an ok result, graduated neutral density filters eliminate the need, and produce more pleasing results strait out of the camera. I spend maybe 5 minutes or so figuring out what filtration to use, and getting it placed in front of my lens. Ultimately, I am more satisfied when I put the time in out in the field to work the scene, find my vantage point, and meticulously prepare and take my photographs. I also enjoy having more time on my hands at home since I am not spending hours working my images just to get them to look "decent". I can now put that time into making them look like "mine"...a stylized, artistic signature of who I am and how I see the world. 

A simple rule of thumb is, outside of basic exposure control and white balance, if you didn't get it right in camera, you generally can't fix it post-process. If your focus is off, if you blow out your highlights or block your shadows (or both in very high contrast scenes), if you didn't compose the scene properly, if you didn't even capture the most interesting scene (i.e. try different focal lengths), then there is little or nothing you can do in post processing to fix it. Basically, post-processing isn't a replacement for good camera work, although it **can** often *enhance* good camera work.

That said, some things can't be done in camera. A lot of stylistic, personal trait, or artistic elements of a photograph can only be done during post processing. While certainly no replacement for getting proper composition and framing, focus, dof, etc. in camera, you have a lot of artistic freedom when working with your images on a computer. The possibilities are almost limitless, from simply pushing saturation to the limit like Marc Adamas, to moderate image cleanup that removes unwanted elements from an image (i.e. using Photoshop CS5 Content-Aware fill to remove unwanted or unexpected ugly objects from an otherwise great photo), to complex photomanipulation that takes elements of one or more photographs (and possibly artificial elements), and blends them together to make something entirely new and unique. 

Post-processing is ultimately a personal choice, and a fundamental element of ones personal style. You can choose to put all your effort into capturing the perfect picture strait out of the camera, or you can put some effort into turning what you capture with the camera into a unique, stylistic work of artistic perfection that is readily and clearly recognized as "your" work. Neither is the "correct" way, neither is the "best" way, any route you take is simply a part of your personal style, a factor of your work.


  [1]: http://www.josephholmes.com/gallery01.html
  [2]: http://www.marcadamus.com/index.php