Large Excel File

What is the largest Excel file that you would produce.

My workplace has 18 MB excel files. That is outrageous. What can Excel handle effeciently. I know Access Databases shouldn't really go over 100 MB. Excel sheet shouldn't go over 1 MB?

Thanks.

What Excel can handle is largely a matter of what's in there. The workbook can still be usable with 50MB or more if it's just data and few formulas. If the workbook is chock full of formulas, especially calculation-intensive ones, like array formulas and lookups over large arrays, then the workbook can get hard to use at 8MB. What's in this workbook and have your reviewed the formulas for efficiency?
Also, if it's saved in a pre-2007 format and you have 2007, you should note that .xlsx is a much more efficient format than .xls and the file size could potentially be reduced to under 5MB. This won't really help with calculation speed, though.