When I edit or synchronize subtitles, I don't touch any of the credits for the original translators etc., but I delete ads for other websites. For me these ads are just spam, they don't belong in the subtitles. Most of them are added automatically. Some of them make the file format invalid (using line number 0). I never add myself to the credits in subtitle files, but I understand when people want to be credited for their work. What I don't respect is the website ads. Sometimes it's a fine line -- when a subbing group is associated with a website.
I want to make clear that when I delete an ad, this is not meant as an action against "competitors" of opensubtitles. What I do is for the community, not for one website. I use other sites as well and I think the more sites there are, the better.
I just got an angry comment for some subtitles I synchronized, where I left the credits in (and copied them to the upload comment field) but deleted the website ads. I would have replied to the comment but apparently it has been deleted by a mod. Still, the question remains. How does everybody else handle it?