Frankly I'm a little hesitant to attempt to explain in too much detail, because I don't want to do a bad job and I'm not sure I'm seeing all the angles. I'll try to do a very high-level view. Keep in mind that this is just my perspective.

The most important thing is that although we started as a very simple profile-plus-friends social network, there are now a very large number of people connected in this manner.

We have the opportunity for the first time to really let a user define their identity in one place [their relationships to real people and entities in the real world, their likes and dislikes], and shape the content on the web around that identity.

We have the ability to share that opportunity with smart hackers everywhere -- but we obviously cannot just willy-nilly hand over the data to anyone. We need to define a usable API, a set of acceptable practices, a way to enforce these things so we respect the user's trust without completely destroying the app developer's ability to do something useful.

This is really hard. We're slowly finding our way to doing this well, but there are many unforeseen issues, especially because app developers have a lot of money at stake. We're iterating on our API, trying to change up the constraints on developers.

At the same time, several cool applications wouldn't be possible if everyone were to keep everything private from everyone -- you have to be social to some extent on a social network if you are to derive any value from it. So we're trying to get people using this complicated privacy interface where you can control publicness/privateness at a very fine grained level, but you need to understand many things to do this correctly.

We're also trying to set things up so that you can hide things as you want from the real people who might judge you for it or whatever, but at the same time, you can get functionality related to that interest from some application [for example, you may not want to tell your friends you like Britney Spears, but Pandora should still be able to play you Britney Spears and similar music].

There's a whole other dimension related to the Open Graph stuff -- building a "semantic web", having one graph where users and entities are connected and organized in a way that can be leveraged to do all these cool things that the web originally promised but hasn't been able to deliver.

There are tremendous engineering challenges to putting all this together.

As you can see, this is a lot of balls to be juggling. Our philosophy has always been to iterate quickly, correct missteps just as quickly, and not be afraid to innovate.

There are a few things I'm pretty confident we don't ever want to do-- the first of which is that we don't want to ever sell user data. That would be an incredibly stupid business decision for a company that wants to help you manage your identity on the web, and we recognize better than anybody that users need to trust us.

I think I've gone on long enough-- I'm not sure I actually answered your specific question. Hopefully my blathering was useful to give you some feel for our motivations though. If you want to learn more, you can listen to some of the talks here: http://apps.facebook.com/feightlive/ . I recommend the closing remarks by Chris Cox.