1. Socialized Everything - all of your content is now easily optimized to be infinitely more shareable and sociable.  Your visitors will not only be able to seamlessly share content, but see what their friends have done.  And while privacy advocates and concerned citizens cry out Big Brother!, the rest of us will use and enjoy this new offering (this isn't to say they don't have legitimate concerns, I just don't believe we as a society will refrain from using these tools for these reasons).
2. Data - 1) Facebook's analytics aren't earth shattering, but if marketers are going to be working with the system it's important that these analytics be paired up with other performance data.  Most importantly, this makes sharing into a site metric, and brings all the rich demo data we get on Facebook into our site data.  Facebook's site analytics package probably won't cause to many large enterprises to abandon their current metrics providers yet, but it may be a compelling alternative to Google for small business. 2) Access to  more than 24 hours worth of data is huge.  Not all activity takes place over 24 hours, this provides a much needed window into the longevity of a social statement.
3. Creativity - whether it's the Graph API, the wall, or even how you position the "Like" buttons, there is an entirely new can of worms available to all.  While at first we can all expect a crop of tools that claim to analyze our social circle and tell us what car to buy or cracker best represents us, someone somewhere will create a wow-worthy integrated application that will blow us all away.
4. Partnership - Credits for one and all.  While Facebook's new currency initiative doesn't provide a wow-factor out of the box, it's future will be dependent on not just it's growing network of partners feeding into the system, but products feeding out of it.  Let's be real.  There's not too much I do right now that requires Facebook Credits.  But if I could cash them out for goods, services or access to... say Hulu's new premium option, we may have something worth talking about - a new cross platform web currency.  Think "Linden Dollars" only useful outside of the barbie world.

• The other nice piece of news for marketers, is that we have an open invitation to engage Facebook, and Facebook has an existing sales and support staff to support these discussions at scale.  Twitter could learn a lot from this.

The bottom line: the more Facebook grows from a tool to a platform to an ever-present companion, the better off Facebook will be in the long term.  Facebook knows how to court partners.  And they are in it to win it.  (Inspired by this post from Robert Scoble). 

PS - all this data, sure would create a compellingly smart search, would it?