I agree that a notice would be nice... perhaps even in the synther itself, rather than on the website, since I certainly never visit the website first when I want to make a new synth.
On the other hand, if a new synth gets to the "Publishing" phase, that means that it has already calculated the entire synth and (I'm almost completely certain) uploaded all the files to the Photosynth.net servers. The only thing remaining is indexing the synth (giving it a URL, listing it in the 'Recently Synthed' list if it is a public synth, adding the description and tags to the search index, etc.
Since everything has made it to the server safely, if we see a new synth get stuck in Publishing, this usually just means that we'll have to wait a day or two and suddenly our synth will appear. Sometimes other synths that we make after the one that got stuck will actually get through first if they are uploaded to one of the less busy servers while we wait for the first.