Here is our scenario:
Developer A checks in changes which include new files files. Developer B does an update and all of a sudden, stuff breaks because files are missing. Developer B tries another update, nothing is pulled in, so he calls Developer A. Developer A says: "Hey, I checked them in, are you blind?" Only when Developer B uses the TortiseSVN Repo Browser does he see that, indeed new files are available. The fix is to 'update item to revision in TortiseSVN Repo Browser. Even if Developer B updates through TortoiseSVN in explorer or the Subversive client in Eclipse, he can't see the new files. We also can't see the file via the SVN command line client in Cygwin.
It doesn't happen all the time, and we can't seem to reproduce it at will. But when it does, it's highly annoying.