Question: Currently I'm rolling my own score and leader board functionality in my FB canvas game.  

In my game, users can see what score they have, in addition I have a public leader board where everybody can see all scores from all other users.(I also have possibility for each user to set themselves as anonymous in the leader board, if desired)

But now I started thinking; why do I have my own leader board system?
Facebook has this scores API and I started play around with it.
It, of course, integrates well with Facebook, scores and achievement showing up in the ticker and what not.

But it seems that I can't let each user see a public leader board in much the same way I currently have it. But it do let the users see their friends score.  

Let's face it, this is all what FB is all about, right? Friends.

So the question is; should i scrap my own leader board and go for the Facebook built in one (and skip the public part of it)?

My gut feeling says yes, but I wanted to hear what other thinks.

Answer: 
I think there are two basic problems with a global leaderboard:

1. [Cheating](https://gamedev.stackexchange.com/questions/4181/how-can-i-prevent-cheating-on-global-highscore-tables).
2. And from a design standpoint, what does it do for the game experience? I would argue it actually detracts from a player's experience, unless a global ranking is somehow achievable. When I finish playing a game for the first time, have a couple hundred points, and then get shown that the top 10 people all have scores above a million, it's not a motivator for me; it's discouraging. It's like an impossible goal. It benefits those 10 people's egos, and detracts from everyone else's sense of accomplishment.

Limiting the leaderboard or high scores table to only friends, though, negates both of these elements. As a player, if I cheat, I know that I'm just doing it to show off to my friends, so I have less of an incentive to cheat (and if I do, you the game designer don't care because it's not globally visible). And it's likely that my friends are of a similar skill level to me, so I feel like I can beat their scores if I try hard enough - and indeed I probably can. Which then motivates my friends to play the game some more to try and beat my score. Which creates more traffic to your game, which is what you want.
I'm a bit late to this question as I've only just started considering the same question myself. I've just launched a game on FB which we created a global leaderboard for, but it also has the option to display just the friends scores. The FB score and achievements API does look good, but I know for my own game (puzzle game) people absolutely want to see who is scoring well in the game across the network, and also what scores are possible. Also if you just make it friends only than unless each player has LOTS of friends who are all playing it, their leaderboard is going to look pretty empty, which I would argue discourages people from playing, for me the more scores people see being posted the bigger inventive for them to do well themselves.

The ideal solution is a global leaderboard and a local one.