At the time I published the original hint, I assumed the author was discussing a truly duplicated Finder, and not merely the existence of the "Fake Finder". After seeing the comments start flowing in, however, I decided to "phone a friend" at Apple for a hopefully authoritative answer on the issue.
The reply is a bit lengthy, so please read the rest of the article for a full explanation of the need for two Finder files. The reply also includes an easy way to recreate your "Fake Finder" if you deleted it based on the previously published hint. The file does have a role to play when using OS 9, so you may wish to make a new one if you did delete the original "Fake Finder".
Here's what I received from my friend at Apple:
The file's a stand-in for the original Macintosh Finder. It's actually zero length but it DOES have the correct Finder Info to masquerade as the original Finder file. From an Apple Engineer who knows the answer, "the file is there so that Mac OS 9 doesn't unbless the Mac OS X system folder in certain cases where it would otherwise want to."So clearly, the "Fake Finder" can have no performance impact on OS X, and if deleted, the only operational impact may be an unblessing of the OS X system folder while running OS 9.
FWIW, the current Mac OS 9 "Startup Disk" control panel doesn't care about this file (nor, clearly, does anything else in Mac OS X - the file's zero-length, after all). I'm not sure whether previous versions of "Startup Disk" care about it or not.
If you need to recreate it (assuming you've got the appropriate Developer Tools installed and on your path), just% touch /System/Library/CoreServices/FinderNo lasting damage done, anyway. Heck, if it REALLY bothers you to see it there, just do:
% SetFile -t FNDR -c MACS -a I /System/Library/CoreServices/Finder% SetFile -a V /System/Library/CoreServices/Finderto mark the file invisible.
My apologies for the confusion stemming from the original tip, and hopefully this explanation will put the issue to rest once and for all. I have removed the original hint and comments associated with it, so as to not confuse newcomers to the discussion!

