I'm gonna sound very jaded when I say this, and I agree that a 478-to-423 socket converter is a good idea (it will be lucrative for the right price), but I think that anyone who bought into Socket 423 made a short-sighted decision and didn't do enough research. Throughout the entire lifespan of the short-lived Socket 423, it was heavily publicised (here at AT and many other hardware sites) that there was going to be a die shring followed by a large speed increase to the P4 as well as other unannounced improvements (which turned out to be the increased cache size, etc). Also, the original P4 (1.3-1.8 GHz) had no real performance increase over the then-current P3/Athlon Tbird platforms, and the RDRAM prices were atrocious at first.
Honestly, I'm surprised there even is a converter for such a changed platform (there have been converters in the past for the Socket 370 platform, but they were to different revisions of a socket with the same # of pins - PPGA CPU's like the original Celeron, then Coppermine cores like the P3 and Celeron II and finally the Tualatin P3/Celeron).
Edit: I just checked out the price of this converter, and $12 is an incredible price! It pisses me off that they can make a converter like this for so cheap, and the Tualatin - FCPGA 1 converters are so damn expensive (probably way easier to make as it's only a voltage change in 2 pins).