Prevent private and/or local-only bookmarks from syncing

It would be good to mark certain bookmarks as "local" or "private" that do not sync online. For example, company intranet links are not only useless at home, there may also be a confidentiality/privacy issue (leaving aside issues of the general practice of syncing work computers to outside servers for the moment). Another example is links that point to local files, such as C:\my favourite document.doc that again are useless away from the computer the link originated from. A "mark as local" check-box would help out a lot.