For me, the answer is, none of the above are quite adequate.

I don’t want to have to search in multiple of these locations for major, minor or trivial updates, especially ones which are time sensitive (alot of them, for different reasons) I’d much prefer to see them all in the same place, and I want that to be immediately accessible whenever I log in. As a small example of the problems – playing dom against players who weren’t aware of the changes to the ties rule was frustrating, both for me when I was offering players ties, and later for those who realised they’d just shot themselves in the foot. So really, I want other players who are considerably lazier than myself to have a fair chance of seeing these changes as well.

Have a look at the way Kingdom of Loathing does announcements. They put some thought into it and it works well, both as a means of disseminating information, and keeping the community energised about the game. The latter is the reason why you shouldn’t be hiding game enhancement announcements in blogs, twitters and flamebate (with multiple forums to check since announcements may be relevant to one but not another, e.g. domination, forumbuildr, the core game)

Something should be on the character page, which players will see if they’re active, but it should be an integral part, and not quite so intrusive as the black bar at the top e.g. a list of major and minor updates in the sidebar, leading to something more comprehensive in a dedicated forum. Such a forum may mirror the blog and/or twitter combined but it needs to be an integral part of the site. Or reuse the tutorial style prompts for game update information, so players can just click the x after having read them.