Also: spam your user base with irrelevant stuff on a daily basis even when they've opted out of every email possible. Pretend it's an "accident".
I'm nearly to the point with LinkedIn where I want to take them to court. What they're doing is a clear violation of CAN-SPAM. I generally feel that kind of thing is a waste of the courts time, but I simultaneously feel that marking the messages as spam in gmail isn't doing enough to curb their annoying and illegal behavior.
And you know what annoys me more? There are probably 10s of LinkedIn engineers on HN who are probably reading this thread and know about this illegal spamming and should know better then to leave that unchecked.