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: 
When you use Excel Introp, it actually opens Excel in the background (You will see Excel in the Task Manager) and it make changes very simular to a user making it directly in Excel. So it needs to be installed on the computer that the application runs on, and set up (if needed). Make sure you clean all the COM references to Excel, otherwise the reference won't be released, and Excel will still be open in the background, even after you close it!
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..).