The talk about the Guardian misstep is all happening in the comments to Who guards The Guardian. To me, it’s clear that Hammersley’s activity as part of RSS-DEV creates the appearance of an impropriety or conflict. The only issue is whether the Guardian’s mention of Hammersley’s book is sufficient disclosure.
Do we assume that authors of books on political campaigns were active participants in a political campaign? I don’t, I assume that they were journalists who covered that campaign. Similarly, do we assume that authors of books on XML were members of an XML group? I don’t, but here’s where it gets interesting – if I were to pursue that query, then I suspect that most authors were members of an XML group at one time.
Turn the question around. If there was a televised discussion about a political campaign, would you introduce a speaker as an author of a book on the campaign or as a participant in that campaign (assuming that both are true). I think that you’d mention both and that if you were forced to mention only one, then you’d go with the participation over the authorship.
On balance, I think many readers would not make the jump from author on RSS to potential impropriety or conflict in discussing the history of RSS. Therefore, the Guardian had the duty to disclose Hammersley’s RSS-DEV membership.