A post in the Microsoft Online Services TechCenter how Microsoft detected the issue and quickly assembled the teams necessary to isolate and troubleshoot the problem. A software glitch was discovered causing an Exchange Online HUB server to get clogged with messages. Microsoft added additional servers to share the load, and at the same time Microsoft is also developing a fix for the underlying software glitch.
Nobody can guarantee 100 percent up-time, so an occasional issue is to be expected. The fact that Microsoft responded quickly, implemented a temporary workaround, and identified the root cause in a relatively short time is also commendable. But, the fact that Microsoft is having repeated issues back to back, and that those issues are impacting email--the lifeblood of business communications--is not good.
Microsoft is getting ready to replace Business Professional Online Services (BPOS) with Office 365. There is no official launch date set for Office 365 yet, but it is imminent. With each BPOS or Exchange Online incident, potential Office 365 customers will be increasingly leery of trusting Microsoft's ability to deliver cloud-based services.
It is worth noting that these incidents have not had any impact on the Office 365 beta which has thousands of users. So, an argument can be made that switching to Office 365 makes sense as a solution to the apparent instability of BPOS.
I like Office 365. I am . Since I left the corporate world to fly solo I have missed having access to the full Microsoft Exchange environment, and I am looking forward to having a once again when Office 365 is launched. But, incidents like these are concerning, because outages and issues mean no productivity, and no productivity is bad.