Sometimes the file size can get huge because Excel thinks you have formatting in every cell on the page. Go to the last column and select all the unused columns and delete them. Do the same for all the unused rows. That should get rid of cells that have unusual formatting in them.

Give an example of a formula so I can see if it might cause some performance hogging.

One other question, what version of Excel, and if it's 2007, what file type are you saving it under (.xls or .xlsx, etc)?

BTW, yes that file size is huge. It doesn't sound like the data in there is enough to cause that kind of bloat.