I have a very simple Excel 2010 file--the names, addresses, and phone numbers of about forty personal contacts. No formulae, special formatting, or complications other than alternating background colors for the rows so I can follow the line from a name to the appropriate phone number across the page. My computer has a quad processor and 6G of RAM, so this file just POPPED open for several months. Then it began to open more slowly, and now opens in percentage increments: 6%...8%...13%...
Asking it to insert a new line gets me the "This action will affect a large amount of data" warning; when I say OK, it then tells me it can't perform this action with the available resources. At that point, attempting to select and delete all cells to the right of or below the active table ALSO gets me the "large amount of data" warning and the no-can-do follow-up. Then saving and shutting down becomes a nightmare--have had to kill the program with Task Manager more than once.
Other Excel files of a similar complexity, and with exactly the same background color scheme--my UserName and Password list, for example--still POP open. I notice also that those files are about 25K in size; the troublesome address file is now at 8.35M.
At no point have I added any special formatting or otherwise tinkered with this file. I wonder, having read a great many similar accounts on the net, if someone has generated a bug that puts a single byte of data somewhere out in the Infinity Corner of the Excel program, compelling it to deal with everything from square one to out back of beyond...