The news from FB are that starting March 11th no developers wil be able to create new FBML tabs. If you market via FB, get ready to the change. The light in these dark news is that all existing FBML apps will be supported
Frankly speaking, the FBML pages are not giving that much traffic, so its better to go off. I have 5 fan pages on facebook on different niche and have kept the FBML application on only three of them. Seriously, I get more views, likes and traffic to the fan pages which are without the FBML pages, only because the visitors like to read and comment on the walls frequently.
Yes you can keep it. The existing FBML tabs will stay as they are. But you cannot create new ones after the date mentioned. I am soon launching my Internet Marketing blog and would obviously need a Facebook page to better interact with my readers. So I'd created the page yesterday, though I've only began work on coding the design for my blog. I installed the FBML app so I can edit it later. If any of you are doing a similar thing, you should pro'bly do the same.
seriously FBML was a pain in the backside anyway, glad they are moving towards iframes FBML pages were only great for landing pages anyway, the best thing about fb will always be user/social interactivity hence the wall and tagging photos etc