• +1 for Phils suggestion. Keep Excel a long long way away from SSIS.

    32/64 bit compatability issues (made more complicated when you develop on 32bit laptops and deploy on 64 bit servers)

    Differences between .xls .xlsx and .xlsm

    sensitivity to sheet names, columns types and all other crap that users change in spreadsheets when they don't know what they are doing (sorry - I mean don't appreciate the knock on effects of their actions). The last one I had lost me half a days debugging: a user had protected part of a worksheet which meant that the .xlsx was encrypted and could not be read by the parser, even though the spreadsheet itself was not protected with a password.