I don't understand why they're moving to full disk encryption. Encrypting the home directory seems most efficient - it encrypts your private stuff, while not wasting time encrypting system folders, etc. If you have content you don't want encrypted (for full speed), you can just put it outside your home folder (like my iTunes media).
It isn't "Full Disk Encryption", rather it's encryption at the disk level, which should allow for file by file encryption, or for files within a specific directory, such as the home directory. There were problems with the current approach which involves a disk image. Disk images can sometimes become corrupt for various reasons, which would then lock you out of your home directory. Filesystem encryption is far safer, and potentially faster.
EDIT: Although FileVault 2 does in fact encrypt the entire drive, it seems likely that you may be able to change that behavior either through the GUI or via command line, however we'll just have to wait and see. The performance shouldn't suffer much, at least based on what they say. I don't know enough about filesystem encryption to comment on that. Common sense says there will be a slight load-time performance impact, but that wouldn't really amount to much.
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