IFrames are not supported with XHTML 1.0 Strict Doctype.
When you use IFrame and your doctype is XHTML 1.0 Strict, then you cannot pass the W3C Markup Validation test. You always get errors.
The errors are like:-

Twitter, Facebook and wordpress are all popular and fascinating. You publish an article in your wordpress blog. And you may want to publicize your article in twitter and facebook through status update separately. It would be very easy and time saving if I could publicize my blog article in twitter and facebook as soon as the article is published.
But this is possible and I have implemented it as well. You just need a wordpress plugin and facebook application.

Facebook Connect is the next iteration of Facebook Platform that allows users to “connect” their Facebook identity, friends and privacy to any site. This enables third party websites to implement and offer even more features of Facebook Platform off of Facebook – similar to features available to third party applications today on Facebook.
Facebook has lauched Facebook Connect with 24 partners initially. Those partners include CBS, CNET, CollegeHumor, Disney-ABC Television Group, Evite, Flock, Hulu, Kongregate, Loopt, Radar, Seesmic, Red Bull, Socialthing!, The Insider, StumbleUpon, Twitter, Uber, Vimeo, Amiando, Plaxo, and Xobni.