Good afternoon Ara Ghajanian,
The PDN Forums is one place you can read about film usage amongst professionals, and some threads newer than the one pointed out above are still ongoing. The PDN magazine also has articles on some working professionals who use film, as does Picture magazine. However, there is a digital capture or perish mentality that happens too often in publications, probably because their advertisers want to push the latest gear.
This issue is often polarized and politicized, and I am a bit surprised at the well thought out responses so far at APUG; it is a welcome change. Unfortunately, this newsgroup forum began as the anti-thesis of too many other digital forums, many of which are populated by clueless amateurs making wild claims. One exception is the Large Format Forum, which gets a nice mix of responses, though overwhelmingly film users.
Defining which professional might show more of how profits are still possible using film, and often quite good profits. There is less need to turn over most of your equipment every 18 months, like too many cutting edge (bleeding edge) photographers are doing. A wedding professional should be able to still use film and meet their clients expectations. A remote location photojournalist needing to send news images via satellite uplink probably cannot do much with film. However, it should be noted that in the annual World Press Photos competition, 12% to 22% of images submitted in the last few years were still on film, and that is from working photojournalists.
Your mention of product photography is a different realm. The needs of very high volumes and fast turnaround created some production environments using the newest technologies. There is also an issue of outsourcing, such as an article in PDN recently about much of the furniture photography industry having product photography done in China, near where a great deal of furniture is made. Large products still seem to benefit from film imaging, so automotive or architectural professional photographers should be able to continue with film usage.
Fine art photographers are a very separate group of professionals, and I would think one of the largest group of film users in the professional community. Selling individual prints seems to not need much of the immediate feedback during capture, nor much need to manipulate images later. Obviously, there are exceptions, and some of those people write articles or run workshops, so they might be influencing some people.
Commercial imaging involved in advertising or corporate work can still benefit from using film, and there are some professionals still making good money that way. When your book is shown to art directors or art buyers, there is no mention of what gear created each image. The results are the emphasis, as I think it should be. Many of these potential clients might want image files delivered to them, rather than film, but they rarely care if you started out capturing to film. This is largely how I work, though I almost hate to mention it here. I would more encourage people who want to figure out how to profit from a film workflow in advertising or corporate work to visit PDN, or the Large Format Forum.
As to film usage, my local lab tells me they have seen a drop in E-6 35mm, an increase in E-6 4x5 usage, and about the same level of roll film in C-41 or E-6. I still shoot musicians in 35mm, even using some B/W films. I also do some advertising related images in 35mm, though the majority are roll film or 4x5; mostly it depends upon the final printing sizes. My editorial work can still be done mostly on 35mm. I don't do any stock photography. I do fine art photography on film, but my sales there are only a little better than break even.
I don't understand the mentality of photographers that some might give a client images at the end of a shoot. Even if it is technically possible, it is not a good work practice. As a professional, you create magic in the images. Show a client everything, then they will see your not so good images; soon your clients might get the idea they can just buy a camera and do it themselves. Editing is a skill, and any client should only see your best images.
Finally, I have been asked by a few clients why I don't capture digitally. Rather than relate that here, let's just state that film still gets the job done, and quite well. I have also been asked a few times: what camera should I buy to take photos like you, to which I state the one with me behind it. Like a few people in this profession, I see cameras just as tools, though the film choices are like choosing different paints.