I've been using mine for work a lot recently. Taking notes in meetings and managing my "To-do" list on it with the Things app. Being able to access the works exchange mail on it is also a bonus as it gives me something to do when the meetings turn dull. Logmein to access my test machine from anywhere is also mega useful. Wouldn't want to be without it now.
Business case for them to be bought with company funds is now being written.
Gally, if you use them for what they are intended, they are impossible to beat. Downsides are that you lack the flexibility and power of a normal laptop, but I have a laptop/ desktop for that.
For instant-on entertainment, they are fantastic bits of kit. Even my two year old can use it.