If you're involved in a message thread where everyone "replies all", there's an easy way to opt out: Smart Mute.
With Smart Mute, which can be
found in Gmail Labs, conversations will only appear in your inbox if a new message in the conversation is addressed to only you, or if a new
e-mail in the conversation adds you to the "To" or "Cc" line. Once you enable Smart Mute, it'll be active across all versions of Gmail—Web,