I can absolutely see Dropbox, Google and Facebook creating a class of SSDful machines as a middle performance layer between RAMful and Diskful machines, but price point and storage limits have a long way to go before there's any wholesale replacement of diskful machines with SSDs.

Also, I'm really surprised there's a datacenter that has a meaningful amount of Facebook, Mozilla, Dropbox and Google servers in the same DC. Looks like someone might be trying to bolster their DC image a bit.