Google's has implemented autosave for posts, using a cookie-based approach just like frassle's. Their announcement also has an update that mentions they've disabled autosave because it causes an annoying problem for some users. I wonder if this is the same issue some frassle users have reported, where they are always prompted to restore a post—even if it was successfully posted? I still haven't figured out what's going on there… do any readers suffer from this problem?

(Perhaps it only happens when you edit? I just got it on editing this post.)