The rebuild does quite a bit and if they have a large folder (vs many small folders) I could see it taking longer than normal. We may have also added newer logic into that since you last rebuilt. It does quite a bit now since its kind of "repair-all" for the mail folder. For example sometimes when we're trying to find a particular message we may need to open or check multiple GRPs instead of just one. We also may have to re-read each email to check it for attachments, signed parts, calendar information, etc. We do have a debug log (only enable this IF you want to debug) '111' that can show this process in more detail.
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com