Elsewhere on this site, Declan O'Kelly reports that an additional five counties have been added to the online database of the 1911 Census. Census data from nine counties is now available online: Antrim, Cork, Donegal, Down, Dublin, Galway, Kerry, Offaly and Wexford. (Note: if you go to the 1911 census web site and see "Kings County", that's not Brooklyn. That was Offaly's name at the time.)
My wife and I recently spent quite a bit of time searching the records of the 1911 census. All of her family was living in County Dublin at the time and we were able to find records for each one of her grandparents' families.
What is particularly good about the digitized 1911 census is that you can view the actual census form that was filled in at the time. You can see your ancestor's hand-writing, etc.
My wife was excited by the fact that her great-grandfather had made a mistake all the way down the form and had to cross off and correct it. She pictured her great-grandmother letting him have it for this, projecting back through time onto her great-grandmother the traits she remembered from her grandmother, who was six in 1911. In addition, my wife learned something new - that her grandmother had been born in County Fermanagh.
I know for a lot of Irish-Americans 1911 is too late for any Irish connection, their Irish family was already living in America at the time. In that case the 1911 census might have little appeal, although maybe aunts/uncles/cousins still lived on the family homestead. If, however, you did have family in Ireland in 1911 the census is a great resource. It'll be even better when they finally finish digitizing all the counties' data.