Maybe this is natural; its a professional management site, and we don't change jobs/titles very often. I DONT use it like facebook at all, and DONT care about social features e.g. Twitter.
This can be great for your career.
If you don't work for a itty bitty startup you can count on someone above you in the org chart catching wind of every LinkedIn update you make. I have been asked about my frequent updates twice at my current job; the second time they were so concerned that I was looking around for a new position (and I had just taken a crucial role in a new project) that they offered me an unasked-for performance bonus following the completion of the project. It totally floored me.
I think that this is probably how it's supposed to work. Long slow periods, punctuated by quick rapid action while people do spring cleaning.