Quickshade stuff that Army Builder make. From my limited exposure to Wargaming over the last couple of years I'm lead to understand that this has taken the wargaming world by storm, meaning that relatively quick and poor paint jobs can be made to look good by simply dipping the model in this stuff.
While I'm all for speeding up painting and making things look good, I have to wonder whether this is a good or a bad thing for the hobby. In the past a good paint job received positive feedback from fellow gamers and this acted as reward for putting in the effort in the first place (not to mention the resale value was always higher). With this quick and simple way of shading a model, you have have to look harder to spot a model that has had more effort put into it, therefore making people less likely to bother looking in the first place.
I guess if you're in this hobby for the back patting you're unlikely to play the games much as the painting would take up most of your time and you'd be aiming for one of the many painting competitions around, but its just a thought.
Personally I'm not sure if I'd use it, not because I think its a cheat, but I'm unsure that giving everything a brownish tint is a good idea or not. I suspect a better effect can be achieved by carefully applying GW washes to specific parts of a model but we will have to see about that.
Anyway just my 2p worth...