If looking at your resume sends the message, "Nothing you can do will retain me," then a lot of good companies won't even bother with you.
Maybe it's their loss, maybe it's yours, but in any case it's an opportunity missed due to jumping around a lot. Debating about it on HN isn't going to change the fact that it happens.
Anyway, I'm just saying, "it doesn't hurt your career," isn't completely accurate. To use your example, maybe it would have been 15 or 20 other recruiters contacting you if you didn't jump around so much.
if you are a true born hopper there is perfect way to do things right - self employed consultancy. it's also paid better most of the time.
and btw getting bored too quickly is terrible, terrible personality trait, for any aspect of life.