Hi Michal!
I currently don't have the spreadsheet-class installed, but will do so tonight. Your code however looks clean, so I don't think that there'll be problems.
Love the implementatio, it's a good benefit.
However I was thinking if we really need a new TempDir setting? Couldn't we combine that with SaveDir?
And maybe we should use @include_once when probing for the spreadsheet file no not generate errors. And if the class was not found, we could set $xls to a string and on the export screen display a link/message that you can use the PEAR-class if you want native CSV/XLS export.
Regards, Garvin.