When querying the ACS 2008-2012, the State Legislative Districts (at least for Utah) are labeled "2010" when using the API and "2012" when using the FactFinder. It looks like the raw summary file data also says 2010.
Using the mapping function on FactFinder for estimates from the most recent 5 year ACS shows current State Legislative districts (effective Jan 1, 2013). This is congruent with what is listed on the first bullet under "highlights" on this webpage: http://www.census.gov/acs/www/data_documentation/geography/
So what is correct here, and what geographies do the most current ACS (2008-2012) 5-year estimates really reflect?