Deffinately Frosty. I plan to do so and be generous with it.  

  Can you stack things on it so the magnet holds them all together.

Yes, some of the advertisements show interesting stacks magnetically held together for welding. 

Frosty The Lucky.

I got brave and welded spoon handles together directly on the face of the chuck. The antispatter spray worked just fine and no spatter stuck to the face of it. The magnets held the spoon parts in place nicely. 

Nice.  I've heard that a strong magnetic field can affect a welding arc.  Did you notice anything different while welding on the chuck?

It didnt negatively affect the welds. It sounded and felt a tiny bit different. Looked normal.