2008 study material is really old for 2011 sitting. As for many of the important subjects like F6 F7 F8 F9 and even for professional level subjects significant changes have occurred since 2008 where some are not just limited to ACCA syllabi itself but also in the standards for example ACCA F7 and F8.
I suggest that if you are going to buy new ones then better buy 2011 edition of books and don’t rely on 2010 as even 2010 edition of books is also old now. However, if you have 2010 books at your disposal and don’t want to buy or can’t afford to buy the 2011 versions than you can use 2010 books also IF AND ONLY IF you know the changes and their affect on the syllabus. Only exception to 2010 edition books is ACCA F4 which has not changed at all and you can use 2010 books also.
So, in short, the best bet is to buy new books.