I don’t think the problem is people linking to TVTropes per se (I’m very fond of the site myself), but when someone starts an OP of “Can anyone think of films in which one of the main characters pilots a speedboat?”, it’s not really helpful when the next response is:
“Here, try this: en.wikipedia.org/Films_Containing_Speedboat_Use”.
The OP clearly has internet access and a knowledge of how to find things on said internet (they did, after all, manage to post a message on the board) and it can, I think, be reasonably assumed the OP has already been to Wikipedia and perused their article on “Films containing Speedboat use”. Further, it might also be reasonably assumed they’ve checked Google, and possibly even the IMDB.
So, rather than requiring “TVTROPES LINK ALERT!”, I think it’s easier to just ask people to refrain from linking to Wiki/TVTropes/etc without any further discussion or explanation; thus providing some context to the discussion.
True, that doesn’t fix the “TV Tropes Will Ruin Your Life” issue, but let’s face it, is is an enormously entertaining website in spite of the overwhelming amount of Anime/Manga discussion. 