Phil Davis has published "PeerJ—A PLOS ONE Contender in 2015?" in The Scholarly Kitchen.
Here's an excerpt:
In my last post, I reported that PeerJ was growing, publishing more papers and attracting more authors, although it was not clear whether the company was moving toward financial stability. In a crowded market of multidisciplinary open access journals, I argued that the success (or failure) of PeerJ would be determined when it received its first Impact Factor, which will be announced in mid-June with the publication of Thomson Reuters' Journal Citation Report. The purpose of this post is to estimate PeerJ's first Impact Factor and discuss its implications.