I check the Baka-Updates Manga site [http://www.mangaupdates.com/releases.html] site every day for new mangas, but I always see long lists of mangas that I've already decided never to read or have finished reading.

AniDB has a blacklist option for animes, so they won't show up anymore in the update list.

On each manga page, BU has an "Add to" option with a dropdown box next to it, containing only 'Complete List'.

I request that an item be added to the dropdown box, called "Blacklist" or "Hidden".

Alternately an option can be added to the user control panel to 'Hide Mangas in Completed List' from update pages.

This way, once a manga is complete or unwanted it doesn't keep showing up again and again. Thus I would only see truly 'new' mangas and mangas that I'm collecting in the updates list. It would be so much faster and more efficient and would also cut the BU server load since it wouldn't have to keep re-sending all the unwanted, redundant data.

You can create a custom list for manga you don't want to read.

Though as far as I know you can't hide titles from the releases page. You can, however, hide releases of groups by ticking the "Hide this group's releases on the Releases page." button in their group page. I can't speak about filtering releases because I haven't tried it nor do I plan to.

Do me a favour and don't create threads for topics that already exist. I see you've already commented here.