I would also wish to have as detailed a description of the advantages and disadvantages of the two as possible...
I use both on different PCs. I have a laptop that is a few years old, and I find OpenOffice annoying simply because it takes too long to load. This brings to mind an interest in finding out if there is a way to prevent certain elements (that I may never use) from loading when all I want to do is put a few entries into a spreadsheet.
Also, as Confused Computer User mentioned, I too have a problem with some spreadsheets which were made in Excel. When I open them to print from OO, they don't print correctly. I can be certain that this is the result of Microsoft's purposeful attempt at 'breaking' compatibility with other applications which might use their documents.
I am not conspiracy-theorizing, I have worked in the PC support field for 12+ years, and have seen that Microsoft routinely does this to maintain the perceived value of their bread-and-butter applications.