At least in R7 and almost certainly earlier You CAN "remove" $UpdatedBy *on design elements*. I guess it doesn't work on regular docs, and for all the good reasons pointed out in this thread. Note that $Updated isn't *actually* removed, but rather all the older values are cleaned out and replaced by the current user name (or presumably server name if run by the server).
This ability is actually quite useful for "cleaning up" a database design that originated from outside your current organization (e.g. OpenNTF, Sandbox, etc.). I can't seem to find an example at the moment to prove this, but I'm pretty sure there are situations when simply signing the database will not completely suppress those annoying prompts to cross-certify "/SomeOtherOrg" which typically appear when first opening a database created by somebody at "SomeOtherOrg". Running this sort of cleanup code on the design elements I believe should further reduce the chances of seeing those prompts. Ytria's ScanEZ has a "Cleanup" function specifically for this purpose.
For those without ScanEZ, I've added a design cleanup script to a special view showing design elements (I hacked $FormulaClass, but that's another story) in my SuperNTF database (http://www.openntf.org/Projects/pmt.nsf/ProjectLookup/SuperNTF
), which is based on code in this thread. The one area I'll probably try to extend the cleanup to is profile documents, which I think may be one of the areas that signing misses, and that might be another reason for the persistence of cross-certify prompts. btw - the code is going to be posted soon as SuperNTF v0.9.5 beta, so if you're reading this today, its not posted quite yet.