I don’t have the fastest USB drive, in fact, it’s probably crapish, primarily the horrible latencies it has.
But when saving a ~450KB .xls file takes 2 minutes, using Excel 2007, something can’t be right. Copying the file to a local harddrive and saving there only takes one second. Copying the file back, another second (more or less). Evidently Excel is doing some crazy seeking whilst writing the file or similar. But why is it so bad??? Surely, these days, it could easily write the entire file to memory before physically writing it to disk?