JISC has just published a report comparing the between XML flavours of standards for office documentation (ie. word processing files and all). It compares ODF with the Microsoft-supported OOXML.
To the layman, the differences seem rather arcane. The real danger seems to be, according to the report, the simple fact that there will be two standards, with different capabilities, in place. This doesn’t make life on the computer as straightforward as it should be.