What he said.

We are warned (repeatedly, in various places including the documentation, the team blog, and here) that this is beta software and we should not place our only copy of irreplaceable important data one WHS. Always have an off-site backup. Even though the team says they will deliver a method of migrating to the final version that doesn't require wiping WHS, we shouldn't rely on that. The wrong bug in the wrong place could make them renege on that promise. I'm assuming I'll have to burn my WHS to the ground when the product is released...