However, it's important that you don't lock all the way up the very latest block. Otherwise, the attacker could generate a fake block (or a few) right before you happen to lock it, and then his attack would be far easier than it would have been without the block lock.
I went about 200 blocks back. The block chain was a clean straight line without branches, and there was only one known version of the locked block.
Also, I'm assuming that the block lock means that the blocks will also come prepackaged with the client. Is this so?
Sorry, not yet, but I do want to make the initial block download faster.