I know that I can output reports to separate Excel tabs using a Report Book, but that's not a good solution when data dynamically determines how many tabs your report should output. For example, I have an invoice report that outputs in the following group hierarchy.
 Invoice Summary (new tab)
[1 to Many] Facility/Department
Summary (new tab)
Detail (new tab)
Ideally, there would be a report property to export Excel in a mode similar to the Web output, where only explicit page breaks result in new tabs. I cannot believe that isn't a more common request. My clients constantly want summary data paired with detail data. If they said data is in the same Excel tab, converting the detail data to a table, de-merges and re-sizes all the columns, which is a difficult to use, ugly mess.