FYI: Just thought I'd point out this new chart to those of you who (like me) use digital cameras as part of your camera kit, and are monitoring developments in the high-end DSLR/MF digital back market. It's a nice little summary of what can be theoretically achieved when lenses match the capabilities of the digital sensor.
While one can quibble with their DPI assumptions (I know some folks prefer more than 200 DPI where possible), in general it reinforces the notion that 31/39 MP digital backs are roughly equivalent to drum-scanned 4x5 film.
Of course, the current generation of digital wide-angle lenses (particularly with regards to 16+MP DSLRs and 31/39 MP digital backs) generally does not resolve to the level of high-end sensors, so the results on this chart often cannot yet be fully realized. Problems currently occur when off-axis light (camera movements) hits digital sensors. The current generation of "digital view cameras" is still rather heavy and clunky when used with digital backs, particularly in the field. And better methods of determining critical focus with digital view cameras are needed (it's hard to confirm critical focus using such a relatively tiny, coarse ground glass, particularly when using movements). So I certainly don't plan on selling my 4x5 anytime soon.
That being said, it will be interesting to see how the digital technology evolves over the next year or so. Then, of course, if only the cost of this stuff would come down..... :-)