An amusing editorial in the neuroscience journal Cortex discusses the excuses scientists use to explain why they didn't submit their peer reviews on time:
Following our nagging for late reviews, we learned that one reviewer had to take their cat to the vet, another was busy buying Christmas presents, one was planning their holidays, an unfortunate one had their office broken into [...] others agreed to review whereas indeed they really intended to withdraw, or were just too busy to reply.
The piece is by Sergio Della Sala, Cortex editor in chief. He goes on to describe one case in which a slow peer reviewer led to an especially frustrated author:
Recently, we received a fuming message from an author protesting that they did not get feedback about their manuscript within six weeks from submission. Messages from this author, rightly displeased by our slowness, became frequent, wordier and more irate as days went by [...] We received a second remonstration at about the same time. This second manuscript was also held up by an unhurried reviewer, who, in an interesting twist of fate, was the very same irate author of the first manuscript.
Della Sala sensibly concludes by reminding scientists that peer review relies on everyone pulling their weight. Since every reviewer is themselves an author, "whinging as impatient authors whilst excusing ourselves as tardy reviewers is not a solution." The problem is that because peer reviewers are usually anonymous (as I think they ought to be), there is little accountabilty for slow reviewers. Just about the only consequence a tardy reviewer might face is to be told privately that they won't be asked to peer review for that journal again. Which is more a reward than a punishment, for people who don't like reviews. However, there are new initiatives such as Academic Karma that might help realign the incentives.
Della Sala, S. (2015). Author/reviewer: A case of split personality Cortex DOI: 10.1016/j.cortex.2015.04.012