Decision to peer-review a paper by author who does not believe in acknowledging reviewers I have been asked to peer-review a manuscript for journal X (field of psychology). I recognised the author name as someone I've reviewed a past paper for last year, in journal Y. The topic of his research is still of interest to me, and before accepting, I wanted to see how their now-published journal Y paper (which I recommended minor revisions for, while correcting several mistakes) looked like - and noticed they did not bother to acknowledge the reviewers. I realised I was put off by this: to my mind it is a question of common courtesy to thank your reviewers by at least including a note in the Acknowledgements. I can see that other papers by this author also lack this 'feature'.

I know we all do peer-review without expecting compensation or recognition - however I feel this is contingent on us not forgetting to somehow thank (if even superficially) each other for what is a rather ungrateful albeit necessary work. This is especially necessary when journals (such as Journal Y) do not openly disclose reviewers' names, nor have any schemes whereby reviewers can add their peer-review contributions to an ORCID-linkable profile etc.

To make up for this (as I perceive it) remaining glitch in the peer-review system, I am myself always careful to thank my own reviewers, either directly if they disclose who they are (as I did in my journal Y review), or at the very least in the Acknowledgements, where I try to make the statement less banal by mentioning a specific way in which the reviewers' comments have improved the manuscript. 

Am I putting undue weight on this, or am I right to think that, if I'm going to devote an entire day (sometimes two days) to peer-reviewing an unknown colleague's paper, and since I anyway cannot say yes to all the requests I get, I might as well do it for authors who don't appear to take this effort for granted?
In my opinion, you are overthinking this.

Academics do many things as part of their jobs, some highly visible, some behind the scenes; some acknowledged, some not.

In addition, social norms vary by discipline, by geography, and by individual. I have thus far once acknowledged a reviewer, since their comments improved a paper of mine signficantly, more so than others with whom I workshopped it with previously. However, I certainly don't write such acknowledgements as a matter of routine. To me it would feel like meaningless boilerplate. 

And frankly, while I do appreciate the importance of the peer review process, fairly often the nuggets of gold are also mixed with piles of dirt -- reviewer comments which, while well-intentioned, are at best of marginal value and yet take lots of time to figure out how and whether to address for at best slight benefit. I think most authors feel this at various times, and so while we recognize the worth of the peer review process overall, and if we are honest also recognize it has on balance improved our paper, our mindframe may not be exactly condusive to writing effusive acknowledgements once we finally craft a reply to comment #17! And it's good to recognize this mindframe challenge when we are playing the reviewer role as well.

Finally, I view the activity of reviewing more as part of my membership dues to my profession, not as anonymous acts of kindness to authors. I feel positive when sometimes (and I don't go out of my way to check) my reviewer's contributions get reflected in the final published paper, but I'm not sure I would notice whether there is a pro forma acknowledgement at the bottom or not.

However, this is a worthwhile discussion to have. I will henceforth set the bar under which I as author acknowledge in this instance lower, since your question has brought to my attention that you, and presumably other people, care about this more than I do!