Question: I have been doing a lot of reading on this topic and most folks seem to agree that having Excel is required to use the COM Interop libraries. However they are never specific as to where that should be installed. Does it need to be installed on the machine I am developing on or does it need to be on every machine that I deploy to?

Thanks in advance,
David

Edit: I should mention that this is desktop development/deployment targeted for all Windows machines

Answer: 
Depends.

If you go client/server and people access the app through their browser, you can get away with having it installed only on the server.

If you go stand-alone, each computer that runs the program needs it.

You'll definitely want it on the development computer as well.
You can also look into using openxml (http://openxmldeveloper.org/) and build office documents without office applications. I do believe you can only build office 2007 or 2010 document formats (e.g. .xlsx ect..).