I lived in Japan for a few months on an academic trip, and at the time I could not bring a scanner with me. I used the DMR, a small 4x5 inch light table and the 100mm APO Macro. The results were excellent. In my experience, the color, tonal range and overall sharpness were not as good as the better film scanners I have used -- the Minolta Scan Multi Pro, Imacon 646 and Hasselblad X5. But it certainly did a great job for the web and for small prints.
If you really wanted to use this technique to replace a scanner, I think you would need to concentrate on a few variables. If you could sort these out, you could likely obviate the need for a film scanner entirely. The most important is the light source -- you need something that is full spectrum and completely even. This basically limits you to the higher end light tables, or fashioning something yourself out of either a very high quality fluorescent tube or better yet, Solux MR-16 Halogen bulbs.
The second important variable would be film positioning and alignment. You need something like a copy stand to really do this well -- something that will hold the camera and lens exactly parallel to the film and make it easy to adjust up and down for different film sizes. Then you need something to hold the film flat -- this could easily just be the top piece of an old negative carrier from an enlarger -- glass or glassless.
Then you ideally need a macro lens that can go to 1:1 or greater. Finally, you need enough resolution to either outresolve the film, or at least come close. You are going to want to have MORE resolution than the film in order for it to look its best (otherwise you will have the artifacts of both the film and digital at the 100% detail...mushy film grain and square pixels...not good). I would not want to use something less than the M9 or 5DMkII -- 18-24mp minimum for best quality...for 35mm. For larger formats you are going to want a lot more. I do think a good setup with a 39-80mp camera would be really interesting -- it would be cool to see how it compared to the X5 for example.
As far as I can tell, the biggest advantage of a true film scanner is that it is easier and faster compared to setting up a truly precision job with a digital camera and light table -- the X5 takes only a second or two to load, will scan a whole strip of film as raw files in a few minutes at 8000 dpi for 35mm and has built in things like dust removal software, film-type specific presets and so on. Most of them are not that great, but overall it is a lot quicker and easier than when I had to do it on the lightbox with the DMR.