Ok, this is not a hack but, since you seem to be building here the wwwthreads of the future (an amazing one) I think it's a good time to bbring back something a lot of people suggested some time ago:
Different trheads should have the trhead title as the "html title" instead of the same title in all the pages. Then you wont overwrite your bookmarks (or be prompted not to) and the bookmarks will be more useful.
As for the hacks... Mi opinion is that all of them should be included. The only one I wouldnt want to have is the language related (that of course should be included as well IMO but that brings the issue of having them "optional". Not much of an issue for me, as I would use all but one, but maybe for other people).
The reason I wouldnt use this hack (or the language feature actually) is that I dont see any "real" use for it...I think someone gave the example of going to an arabic board and being able to post (by using the languages feature). I believe you wont be able to post in that board anyways, but not because you dont understand the menus but because the actual content of the board is in arabic (so you would not see any reason for posting, and even if you do, it's unlikely they will understand you...).
Of course there may be an example of a board targeted to multiple cultures/languages where this would be more useful but I have not seen that yet...
regards (I wish I already had that cool one-touch smiles here...)
