LinkedIn decides they can effectively own anything you publish there

My takeaway is that I will not use their messaging system for private conversations if they get a license to "analyze, use and commercialize" what I am talking about.

Gmail is different:

"9.4 Other than the limited license set forth in Section 11, Google acknowledges and agrees that it obtains no right, title or interest from you (or your licensors) under these Terms in or to any Content that you submit, post, transmit or display on, or through, the Services, including any intellectual property rights which subsist in that Content (whether those rights happen to be registered or not, and wherever in the world those rights may exist). "

MySpace looks different too, note 'private' part which is mostly what irks me about LinkedIn's wording:

"you hereby grant to MySpace a limited license to use, modify, delete from, add to, publicly perform, publicly display, reproduce, and distribute such Content solely on, through or in connection with the MySpace Services [... ] except that Content marked 'private' will not be distributed by MySpace outside the MySpace Services and Linked Services. This limited license does not grant MySpace the right to sell or otherwise distribute your Content"

There's nothing unusual in that agreement. It sounds like every other social network. It's a non-exclusive license to use the work you post on their site. Meaning you can't sue them for copyright infringement for sharing what you've posted on your profile, even if you change your mind. A license is not ownership, and the non-exclusive part means you are not giving up your right to make licenses with anyone else in the world.

Non-story; every Web 2.0 site puts this in their TOS to prevent copyright entrapment by users, then adjusts it when the mob complains.

I assume this is the case by default whenever I publish anything to a social network and act accordingly.

Sounds like a lawsuit waiting to happen is all to me.