I've seen and experienced only PPT 2004 crash, not Excel. Actually, it did not even launch the first time. The remedy is to reinstall Office (sometimes twice). Then it works. It would be great if Apple would be able to remedy that for good.

Alex
3.1 GHz 13" MacBook Pro 2015, 8 GB RAM, OS 10.11.2, Office 2011, TimeWarner Cable
2.8 GHz Xeon Mac Pro 2010, 16 GB RAM, OS 10.11.2, Office 2011, LAN