This really solves all issues of interoperability on the spot. Of course if we are going to have lots of vendors instead - then implementation issues will arise.
Users range from the data entry clerks and subject matter specialists to the topic map creators.
Let's not be too tough on users. Alot of them are much smarter than given credit - and they appreciate being able to review underlying semantics when it is important to their process. See our HR-XML implementation to see how the angle bracket tags context is exposed to the end user. Notice if they can see such detail they can resolve semantic disconnects. I also see that IT staff need at least a fighting chance of debugging the 'MS Word' level of the world.