It's looking really good. Sandia ran simulations, found a sweet spot, and recently ran a test in which they magnetically crushed a liner without fuel. That test worked out exactly how the simulations predicted.

They have several other tests to do and plan to do a complete test by the end of 2013. If it still works the way their simulation predicts, they'll approximately hit breakeven.

The next step will be to build a machine several times bigger. According to the sim, that would take us from breakeven to a 100x to 1000x energy gain (depending on how powerful they make the machine.)

Such a large gain helps a lot for turning it into a practical plant. For one thing, they'd only have to fire a shot every ten seconds or so. NIF's laser approach, by comparison, would require ten shots per second.

Fusion power is actually already above break even. There are a lot more practical engineering problems with fusion power before that means anything, though. Most of these problems have to do with materials science: Plasma is incredibly difficult to contain, and it's very difficult to design a cooling system that could work sustainably. Without a cooling system, there is no way to make use of the heat generated in fusion.

My guess is that if you achieve sustainable output beyond breakeven then it's a more reasonable engineering challenge to scale that up. The key here being sustainable, none of these technologies are too close to that yet it seems.