But there's other sites using the HN name, presumably without permission (e.g. hackernewsers.com). Surely if PG did sue, his case would be quite weak.

It also occurred to me that hackernews.in is clearly a website aimed at Indians, so I don't know to what extent US law applies.

Anyway, it seems that the name is going to be changed, so this whole trademark point becomes moot. http://hackernews.in/item?id=375