A 4000dpi 35mm scan translates to roughly 5640 x 3760 pixels, which is roughly 21mp. Whether all the 21mp of info is useful, or most of it being grain is another issue. For practical purposes, I believe 6-8mp is more than enough.
The original Luminous Landscape's "Film vs D30" was more skewed towards digital, wherease the 2nd one which has the D60 competing against 35mm film and medium format tends to be a bit more objective and neutral.
The thing about digital is the lack of grain, which lends itself well to interpolation to produce nice big prints. I've seen 10 x 15" and 20 x 30" prints from the S1 Pro which are very impressive. And I've also personally printed 10 x 15" from a D30, which is rather impressive too. As far as film goes, I've got 6mp film scans of Provia 400F and Velvia printed up to A4 size and they do look great. Have not tried A3.
I asked a local lab how big can a 35mm film be enlarged to, and the reply was that given a fine grain film, the maximum practical size is probably around 10 x 15" or so. Beyond that, grain might become an issue, but on the other hand, very large prints are seldom viewed close up.
in the meantime, I've found the website which discusses the film vs digital debate. I guess its mattering less and less because theres no doubt that the current crop of 6mp DSLRs can print to A4 comfortably (and so can 35mm), and A4 printing is about the limit for most people...