You can use 3d references to refer to the same cell on multiple sheets if you want - eg:
=SUM(Sheet2:Sheet4!A1)
will sum all the values in cell A1 on sheet2, sheet3 and sheet4
Of course, this is only useful if data is in the same place on all sheets....
Rgds
Geoff
"Some cause happiness wherever they go; others whenever they go."
-Oscar Wilde