When I first got my whiteboard I also used it for writing only, like most people do, I think.
I still use it for writing and I think it is really good to be able to show different points in different colours.
In German, which I also teach there are male, female, and neutral words. In our books they are shown in different colours - blue, red and green and now I can use the same colours on the whiteboard.
The novelty of being able to write in different colours has made my pupils a lot more eager to come to the whiteboard to write. Before this they were always afraid of making mistakes on the blackboard. Now they know that it doesn't matter - they can take it away in a fun way.
Like Phil I also use my whiteboard to watch films, and sometimes comment and write but I also use iTunes and show my pupils SKY News Active Seven Days and then write comments, words or questions to help the pupils talk or write about the news.
I'll tell you some more ways that I use the board later.