My company is an interactive agency. For a few years now as a standard
procedure we've created favicons (favicon.ico) for websites we build.
Recently, we have started creating an Apple Bookmark Icon
(customIcon.png) as well.
As an owner of an iPhone I dig the bookmark icon. But in day to day
browsing on a computer I actually use the favicon. In fact all my
browser bookmarks are simply the favicon. It allows me to have more
bookmarks without displaying any text.