The Daily Camera's Laura Snider wrote a very good piece on the Boulder audit at New election audit targets close races - County is the first to use a 'risk-limiting' audit.

See all the data and results of Boulder's audit for lots more details.

I think we were the first in Colorado to do a risk-limiting audit, and one of the first in the nation, but I know that e.g. in California's Marin county last February Philip Stark did a risk-limiting audit of a ballot measure, and his team is doing them in 4 counties (Yolo, Humboldt, Marin and Santa Cruz) for the recent general election.

I should also update my previous article on Audit Problems in Colorado, where I said that the Colorado audit rule doesn't require an audit of the actual counting process. As a result of the lawsuit last year, the Secretary of State did require, as a special condition of certification for several election system in Colorado, that counties audit some contests for a single actual election-day mail-in batch. I'm looking forward to seeing how the counties actually implemented that. See the conditions of use for the details.