Neowin spotted lots of leaked screenshots of Microsoft Office 15. You can check it out here and also here.
Winreview.ru has gotten its hands on a copy of Office 15 and has taken a long look at what the platform has to offer so far. Despite being an early build, the reviewer states that it is rather impressive; the build number for this leak is 15.0.2703.1000.
While there is not a drastic difference in appearance, there are small updates that the reviewer points out. Things such as dynamic interfaces, small updates to align more with the Metro stlye, and that it is being built on .NET Framework 4. The reviewer also likes the updates to Outlook and notes that there are new transitions in PowerPoint as well.