Excel allows you to configure it to show each open workbook on the taskbar
(Tools-Options-View). At times this gives Excel the look and feel of being
in a separate process. Unfortunately, if you forget and hit the close Window
(x) button in the top right and do not read the warning messages closely
enough - it is all too easy to close more workbooks than you intended and
lose data.

I'd like to recommend that there is at least an option to treat the close
window request as a close workbook request and not close all windows. This
would also happily be coniststent with the other Office products.

While I "know" the way this works I still cannot count the times I've lost
data by quickly opening another workbook for reference and then closing and
losing the data I'd been working with in my primary workbook...