If I run the rebasing tool (client or server) multiple times, will single instance appointments be moved more than once?
Single-instance (SI) appointments that have been touched by the tool have the time zone information (TZI) stamped on them, so they won't get moved again. Where you run into problems is if you run the tool, create a new appointment using the new DST2007 rules, and then run the tool again. Unfortunately, the new appointment created with the new rules will not have the TZI stamped on it. So the subsequent run of the tool assumes it was created under the 2006 rules, so it moves it (incorrectly) and stamps it.