I guess I fit in the "professional whatever" group, though my background is primarily in web design ...
I currently use LR in my job as creative director for a travel company. My company uses a lot of photography but I'm not the photographer. Our images come from a wide-range of sources -- everything from professional photographers who send us huge TIFs or DNGs, to amateur photographers who send us 1.5 mb jpgs, to images from several stock photo services when that's our only option.
One of my jobs is to catalog and edit our photos to suit a variety of needs: different sizes of jpgs for our web site, larger format TIFs for print ads and brochures, PNGs and JPGs for flash slideshows and desktop presentations, you name it. I also have to integrate our library of "old school" images that go back as far as 1' years in with our latest photos, so there are a lot of scanned prints, scanned negatives, early generation Photoshop images, jpgs, tifs, and even BMP photos that still are in use. My long term goal is to use LR to "simplify, simplify, simplify!" our photo cataloguing and editing process. Whether or not that's even possible remains to be seen, but I'm working on it.