Thanks a lot for bothering to explain the problem. I have never seen this in my field (theoretical computer science), so I wasn't really aware of the problem. (

Thanks a lot for bothering to explain the problem. I have never seen this in my field (theoretical computer science), so I wasn't really aware of the problem. (More accurately: reviewers may ask why you do not compare yourself to arXiv preprints, often with indulgence if they are recent, but I have not seen this culture emerge of posting half-baked results to arXiv to claim priority.) It appears that we agree that the problem is not with arXiv. Part of the problem is unsolvable: if prestigious groups can announce what they are working on and discourage other groups from working on the same problem, this may just be reasonable self-interest from the smaller groups and can hardly be avoided. As for reviewers asking for comparison to these works, I guess the problem lies with the reviewers: if an arXiv preprint has not been refereed and/or is hard to reproduce, it should be OK to say so in another paper and not be blamed for the lack of comparison. In any case, this is an interesting problem, thanks again for making me aware of it.