So if someone posts an access-locked entry and a user wants to bookmark that, should only people with access to that entry be able to see the bookmark

I think this would be pretty awesome, personally.

is there anything on the list of "Future functionalities" or anything that I haven't yet thought of that you think is needed for a version 1 functionality?

Sub-bundles, please! I'd like to be able to put my bundles in broader bundles for better sorting. I'd also like to be able to use combinations of tags to search for bookmarks (that is, search my/circle's/everyone's bookmarks for entries tagged with tag1 AND tag2).