New option perhaps in GMail under "More actions" called "mute"?

It has been there for a while, it's not new. You can use it to make some conversations skip the inbox.
I use this for group lists, when there are topics that I don't want to see, I mute them and new messages do not appear.
More about this:
mail.google.com/support/bin/an ...

It was indeed already long time available via a short key 'M'.
Now it's more in the picture...

Mute was introduced in October 2007 when Gmail 2.0 launched!

Yeah, it's really old..
I'm surprized you've seen it just now.. :P

Nope, Mute has been available since 2006:
bladam.com/main/entry/gmail-mu ...