I ran this poll a couple of weeks ago on Twitter. I was looking to back up a theory of mine with some data, however bad my sample set is (people who follow me on Twitter). In the end, I got some data, but I'm not sure how valid it is.
I can't imagine many likely scenarios where you would invest money in a SAN/NAS (where performance is key) and then lose performance (money) on disk encryption. Full disk encryption protects primarily against physical attacks and your SAN/NAS should be in a secure environment.
This was cross posted from my Peerlyst account. I'm really interested in people's perspectives on this, but I've had to largely disable comments in the blog due to blog spam. If you have something to contribute, hop on over to Peerlyst and comment there. I'm really interested in perspectives on this issue.