I use vmware fusion solely to run office 2010 and internet explorer. Here's why:
Office - although I like office 2011 a LOT, I make a ton of presentations which have to work without compatibility issues on other people's presentation machines. The only way to GUARANTEE this is by running office for windows in compatibility mode and saving documents in their native 1997-2003 file formats (.doc, .xls, .ppt - not .docx, .xlsx, .pptx). I have been using this system for years and still have not had one compatibility problem (picture or video not loading, font looking different than I made it, animation not working, etc). Given that it is always backwards engineered, I will never trust mac office to work correctly 100% of the time, hence, I run office for windows.
Internet Explorer - some terrible terrible websites only display correctly if IE is used. The most prominent example is outlook web access and other very old sites. Given that I unfortunately have to visit these sites from time to time, I keep IE installed for that rare occasion.
BTW - running vmware fusion allows the programs to run in their own windows so you don't need to restart the computer. Its great.