The only time I use MS Office is at work. I even have Portable Open Office on a USB drive so I have it everywhere I go (try doing that with MSO!)

The user interface of OO is a bit different, but for the casual user there is little difference. I have Excel spreadsheets with LOTS of custom macros and VBA code that still work in OO. And, you gain PDF creation (which MSO something has added). If you want to ease the transition, you can set the default doc types to be MSO doc types (.doc, .xls)