This question was extensively discussed in a Kudoz question a few months ago, and I don't think anything can usefully be added to what was said then.
http://www.proz.com/kudoz/English/general_conversation_greet...The short answer is that "data is" and "data are" are both acceptable nowadays. In non-academic contexts "data is" tends to predominate. "Data are" is still widely preferred in formal writing. If "data" applies to information which is seen as plural in sense, a plural verb will tend to be preferred.
It is generally (not universally) agreed that "data is" is acceptable (this view used to be rejected). It is definitely not generally agreed that "data" is always singular.