In terms of the material being out of date, this is definitely more true with every passing month. A full list of all of the incorrect material from the Home Office study materials, along with the corrected information, can be found at
http://lifeintheuk.net/index.php/resource_post/keeping_the_life_in_the_uk_test_up_to_date/.
Morre importantly, lots of the contact details for key organisations - Such as the Passport Adviceline - listed in the book are out of date as well. An updated list of contact details for all of these organisations can be found at
http://lifeintheuk.net/index.php/news/up_to_date_contact_details_from_your_study_guide/.
In terms of taking you test, the UKBA / Home Office advise that you should learn the material as reproduced in the study materials - they also say that you shouldn't be tested on out of date facts, but I would strongly advise erring on the side of caution here and learning all the official materials as printed, up-to-date or not.
It's certainly the case that a new edition of the study materials is due from the Home Office. That said, the focus of the Coalition government is currently on managing immigration channels and limiting the number of entry visas granted. I'm sure we're all familiar with the idea of cutting 'net migration to the tens of thousands, not hundreds of thousands' by now?!
The problem is that people achieve ILR and naturalization years after they enter the UK, so it seems that the government is prioritising limiting the number of entrants to the UK now and worrying about how they settle/naturalize later on.
It's also worth noting at this stage that there is a census due next year, so a new edition may be forthcoming once they population and demographic data has been updated. Now that Earned Citizenship has been abandoned this is the next natural landmark that would directly affect the test.