There have been a number of changes released to the Summon service today.  Three that will be noticeable include:

a) Open Access
OA materials are now identified in the results, and can be selected via a facet. Quotation from Proquest:
There are currently over 200 million items in the Summon index that are identified as Open Access.  We will be continuously updating this content on an ongoing basis based on feedback from the customer community and as we cooperate with more providers to properly identify open access content within their collections

b) Discipline scoped searching
Users can now limit and pre-filter searches to specific disciplines using the Advanced Search form.

c) Citation formats
Chicago 16th Edition (Notes & Bibliography) footnoting citation format has been added.