Whilst the books are online, the descriptor for each collection on the respective search screens seems to be providing information for the actual forthcoming household schedules, and not the enumerators' returns. I've had a quick play, and searched for my great great uncle James Paton in Croydon - he is in fact listed as "Mr Paton", and the search only worked when I put in the surname and input Croydon into the "Registration District" field - not the "Lived In" box.
An interesting addition, and good quality images from what I have seen - but not a patch on the original schedules which will be of much more use when uploaded in the next few months.
Click on View All New Records on the home page to access the respective search screens.
UPDATE: Audrey Collins from the National Archives at Kew has added an informative background piece on the story behind the creation of these returns at her The Family Recorder blog at http://thefamilyrecorder.blogspot.com/2010/12/1911-census-enumerators-summary-books.html?spref=tw
FURTHER UPDATE: From Ancestry "The complete set of 1911 Census record images will launch online at Ancestry.co.uk in early 2011, followed by the indexes, which will be made available in sections throughout the remainder of 2011." A new 1911 site page is available at www.ancestry.co.uk/home/new.aspx?o_iid=44806&o_lid=44806