In an article on nathanneil.com there are some valid points about how the system works should any circumstances change. The first being what happens if the organisation wishes to leave the Office 365 service for something else. How will users be able to keep their data, emails and even retrtact any domain name they have linked to the service.
Another potential problem that could occur is when an employee leaves. What happens to their account (emails & data)? The article suggests that the organisation would be required to continue paying the subscription for this employee to keep the data secure and available.
A third point to note is that Microsoft say Office 365 can encrypt your emails, which is essential if you are in the medical or legal fields, but it will only work if you buy extra equipment and have an IT professional that is trained and experienced in connecting the rights management system to Office 365.
A fourth point to note is that although Microsoft offers a 99.9% uptime, this is only scheduled uptime. This means that Microsoft could give advance warning of any scheduled downtime. This time would not be included in the guarantee. The message here is that the organisation would not have any control over any downtime, and this ultimately could cause disruption to its staff and or students. I posted a question about this to the Office 365 community, here is the link: http://community.office365.com/en-us/f/148/p/5707/22878.aspx#22878.