USPTO now requires an examiner to conclude that an element or combination of elements represent well-understood, routine, conventional activity only when the element(s) is widely prevalent or in common use in the relevant industry. This determination is distinct from patentability over 102/103 prior art. The examination procedure now requires: (1) a citation to an express statement in the specification or to a statement made by an applicant during prosecution that demonstrates the well-understood, routine, conventional nature of the additional element(s); it cannot be based on the fact that the specification is silent with respect to describing such element; (2) a citation to one or more court decisions noting the well-understood, routine, conventional nature of the additional element(s); (3) a citation to a publication (book, manual, review article, or other source); (4) statement that the examiner is taking official notice of the well-understood, routine, conventional nature of the additional element(s); this option should be used only when the examiner is certain based upon his/her personal knowledge.
Full text of the memo is available here.