According to The Document Foundation, this version is considered the most stable version of the program and it estimates that over 80 million people use LibreOffice, including large enterprises and government agencies.
LibreOffice 5 serves as the foundation of the development for mobile applications. Its expected that by the end of the year it'll be released a web based version of the program, giving support for live collaborative editing features.
80 million is already a large user base for sure, but it still exists a long way to go. According to data from Microsoft, Office users reach more than 1.2 billion. I believe the transition depends in part from an education process.
The issue of compatibility with Office documents is something extensively discussed. There's no way to be able to reach full compatibility on what already is difficult even to maintain. The Office's formats are proprietary, that means they are binary codes that are not publicly documented and don't follow an open standard. Any individual but the company which created it, this one which has exclusive rights over the format, has difficulties reading and modifying the data in the file. From the user's perspective, it implies dependency in one single company that owns and has exclusive control over the user's data on what it's called vendor lock-in.
Can you imagine if the HTTP protocol was proprietary? If the email protocols were proprietary? If the whole TCP/IP layer was proprietary? We wouldn't be able to access the web using the browser of our choice, even more, we would need computers with different hardware implementations and a licence just so we could connect to the internet. The web wouldn't be a friendly environment for user created content. Instead of sharing knowledge, we would only be allowed consumption. People would be segmented based on pre defined criteria that wouldn't make sense at all, such as geographical location, hardware type and internet plan. Nobody would be able to understand each other. There would be no communication or it'd be very limited, the sense of community as we know it today would never have existed.
But that's what already happens when proprietary formats are used, when people assume everybody else uses Office.
About Office, I see no point in using it, given that Microsoft packs together with the software code that limits and ties users to its product, negatively affecting their experience with the program, like for example DRM, which harms the users, because it was never made with the users' interest in mind. So you're deliberately installing routines that are against your interests.
LibreOffice, like every free software, has a comprehensive license that de facto protects the user's rights. You'll always rely on free software with the confidence that it works side by side with you, not against you. You have the real sensation that the software belongs to you and that it is you who are in control. And for those who know this feeling of empowerment from the tool, we are not easily tricked by promises such as commodity from proprietary counterparts.