Me is also working on Excel sheets at the moment.. But I am using Spreadsheet::ParseExcel (it was posted somewhere here)
a simple "$oWkS->{MaxRow}" or "$oWkS->{MinRow}" does what you want
I like the way I can handle the excel sheet because its quite easy to use and doesnt has any strange features I am not understanding anyway ;-) In fact I DONT want to know more about Excel stuff than rows and columns. Real Database for president!!
Parsing 20mb big excel sheets is no fun at all :-(