Many different kinds of applications can benefit from multi-core parallelism, including add-ins to Microsoft Office.
Donny Amalo wrote a paper, PLINQ and Office Add-ins, where he demonstrates how to implement two parallel Microsoft Office add-ins using PLINQ:
A parallel Monte Carlo simulation add-in for Excel
A parallel custom spell checker add-in for Word
(This paper and many more are available through the Parallel Computing Developer Center on MSDN at http://msdn.microsoft.com/en-us/concurrency/ee851578.aspx.)