> What's btrfs' SSD story? ZFS gets some amazing performance improvements if you add an SSD for the ZIL or as L2ARC, does the btrfs architecture have any similar parts that could be farmed out to an SSD?
Yes. There are a couple of ideas here -- one (as yet unimplemented) is that you could use the SSD as a caching frontend to larger, slower media behind it. Another is that you could use exclusively the SSD to store metadata items; btrfs doesn't care how far away from data you put its metadata, or even if they end up on the same device.