When I started looking at the recent push by developers to bookmark or become a fan of an application, I quickly realized there was no publicly available information about the number of bookmarks and what applications were being bookmarked the most. In recent discussions about platform changes, the Facebook team noted “At the moment we are not planning to make whether an application has been bookmarked query-able via our APIs.”).

Only since the beginning of this month has Facebook provided a way for developers to know how many users have bookmarked their application. Much like I looked at Fans per Monthly Active User (MAU) as a way to benchmark your ability to connect with users, a developer can now look at what percentage of MAU are bookmarked. But even this data doesn’t provide much detail as to how many of those bookmarks are actually visible in one of the current six available spots at the bottom of each Facebook page.

So how are users responding to all these requests to bookmark and what are they doing? I took a very non-scientific and not completely representative sample (42 of my friends and family) to get a very rough idea of what’s happening. The results surprised me: about half of the users had not taken the time to change the default Facebook bookmarks.

There are six visible bookmark positions on left hand corner of the Facebook footer, but five of them are pre-populated with Facebook applications by default: Photos, Groups, Events, Marketplace (new since March) and Notes. [Note: If a user uploads a video, then Videos is inserted between Photos and Groups and Notes is dropped; also if a user manages or has their own Fan Page, they will have “Ads and Pages” as the first Bookmark, pushing Photos and other defaults down a notch].

When a user bookmarks an application, the icon for that application slides into the sixth bookmark spot. After that, every new application bookmarked replaces the bookmark in the sixth spot (e.g. if you had FarmVille in that sixth spot, then are asked to bookmark Pet Society, Pet Society replaces FarmVille). And that’s exactly what over a third of respondents are doing – leveraging a single bookmark spot for a non-default application.

This split was pretty similar across gender line – but users who considered themselves frequent game players definitely were more proactive in adding more non-default applications:

• Self-defined heavy game players had modified 3.67 of the six bookmark slots
• Medium game players modified 2.27 of the six slots
• Low or non game players modified 1.16 of the six slots

While some of the heavy game players had not figured out how to manipulate the bookmarks (just adding a single non-default app in the sixth spot), over half of them had modified five or six slots. Anecdotally, most game players tended to play ONLY the games that were in their bookmarks, rarely straying to play something not readily visible either through a bookmark or in their newfeed or notifications.

What applications appear to be breaking through?

Some 60 different applications were bookmarked and visible to these 42 users. The top non-default applications bookmarked (showing percentage of all users that had it in their top six):

• FarmVille (26%)
• Mafia Wars (21%)
• Café World (14%)
• Bejeweled Blitz (10%)
• Farm Town and Cities I’ve Visited (7%)
• And ten more apps were at 4%

For more stats and analysis, read the full post at InsideSocialGames.com