In both the full-screen and minimal bookmarklet, sharing to a private group doesn't change the privacy settings for the bookmark I'm about to share. Perhaps I'm missing something, but doesn't this destroy the whole purpose of having private groups? The current setup seems counterintuitive, and, frankly, dangerous.
What I'd propose: when I select a private group via dropdown, then the 'Keep bookmarks private' setting becomes checked, and then disabled (and / or add messaging that explains that this group is private). If you can't make sharing privately an all or none deal, at least automatically select the 'keep private' checkbox.
When I try to send a bookmark to a group from the home page listing, the Group window that pops in is fixed in size and shows only so many (6 or so?) of my Groups (I have 13). Shouldn't I be able to scroll through the list or otherwise select from my list?