In accordance with Facebook’s constantly changing interface, usability and features, they have rolled out yet another update: the pending death of FBML (facebook markup language or the code that creates the pretty pictures you see on facebook pages- for you non techies out there) and tabs.
This announcement freaked me out almost as much as when, a few weeks ago, my fan pages updated moving my beautiful tabs from the prime real estate of the top of the fan page, to just below the profile picture. Now it makes more sense, Facebook is doing away with FBML and tabs – my freak out was part of their plan all along.
“With our recent launch of Requests and the support for iframe on Pages Tabs, we are now ready to move forward with our previously announced plans to deprecate FBML and FBJS as a primary technology for building apps on Facebook. On March 11, 2011, you will no longer be able to create new FBML apps and Pages will no longer be able to add the Static FBML app. While all existing apps on Pages using FBML or the Static FBML app will continue to work, we strongly recommend that these apps transition to iframes as soon as possible.”
To translate: If you have FBML on your page now, it WILL continue to work so don’t fret. That being said, they strongly recommend transitioning to iframes ASAP. That’s a pretty vague statement if you ask me Facebook. So you’re saying my apps will work…but that I should change them soon, thereby subtly insinuating that they may not work in the future? Hm. Not so wild about that statement. Apparently though, we’ve been assured that they will give us plenty of warning before officially killing our beloved facebook markup language.
Anywho, we’re all safe for the time being and it’s pretty easy to switch your FBML to iFrame: Just go to the application’s profile page and under Page Tab Type click iFrame instead of FBML. 
The bottom line (so far as this preliminary knowledge goes) is this: All Facebookers were not created equal; most are not developers. As a result, not everyone will be able to customize a page without using a third party application. To be honest though, that’s nothing new. Average users don’t know how to work facebook applications so for them, nothing will change. What’s GREAT about this though is that now, we’ll be able to more effectively track clicks and conversion (who doesn’t love the idea of Google analytics in your facebook application). Woo hoo! So in sum, this is a good thing from a business/developer point of view but not so great from a regular person pov. If you’re proficient in html – awesome. If not, well, time will tell. As more info comes, I’ll be sure to update!