If you're used to working with keyboard shortcuts, those will mostly work the same as before and, as I said, there are addins available to give Word the toolbar look & feel of Word 2003. Do be aware, though, that if you don't upgrade you'll be unable to share documents that use the newer features (e.g. content controls, citations & bibliography, etc) and this will increase over time.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]