We just started using O365 for CRM and Yammer.
CRM is picking up for sales pipelines, sales forecast etc, and slowly moving to do project management, timesheet etc with the PSA module, currently the free one as we are still in the beginning phase on using CRM (http://www.assistancesoftware.com/psa/licenses/)
Final target would be to use CRM as an all in one place for project management, sales forecast, and probably use the service module as a basic ticketing system as well, but a long way to go as it is still new and people are just getting to know the system.
Yammer on the other hand is just for knowledge sharing, more of a corporate facebook alternative, which again we are planning it very carefully as the last time we tried (free Yammer), was just total chaos as people starting posting anything and everything and literally tried replacing FB in the office in the beginning and then totally stopped. New O365 Yammer, we are using mainly for news on whats happening on CRM portal for example, other news in the company, tech news etc.