When I was watching the address I wondered who yelled that. It was said when Obama was bringing up the point that health care legislation won't support illegal immigrants. South Carolina Rep. Joe Wilson shouted "You lie" after Obama said extending health care to all Americans would not mean insuring illegal immigrants.
While Biden states the outburst has "demeaned the institution," and other legislatures have complained about it, "There'll be time enough to consider whether or not we ought to make it clear that that action is unacceptable in the House of Representatives," House Majority Leader Steny Hoyer, D-Md., said late Wednesday on WTOP radio when asked about possible punishment for Wilson. "I've talked to Republican members who share that view." In all honesty, it's politics as usual. Here are Dems booing Bush at State Of The Union address.
http://news.yahoo.com/s/ap/20090910/ap_on_go_pr_wh/us_health_care_heckling
Democrats Boo Bush At 2005 State Of The Union
http://www.realclearpolitics.com/video/2009/09/10/flashback_democrats_boo_bush_at_2005_state_of_the_union.html
As for the insinuation of calling a President a liar...
Obama Accused Bill Clinton of Telling 'Bald-Faced Lies,' Reporter Says in Book
http://www.foxnews.com/politics/2009/06/02/obama-accused-clinton-telling-bald-faced-lies/
So it's Politics as usual really when you think about it. Personally, I wish our legislatures acted more like the British Parliament (or EU), it would certainly make CSpan more interesting!