Totally agree - that's exactly what LinkedIn is - It is a replacement for the Rolodex with a few key advantages.
1. People keep their email addresses reasonably up to date, so I can contact them if they change their info.
2. Somewhat useful - people keep their jobs/companies they are working for up to date.
3. If someone introduces themselves to me in a business context, one of the first steps we take is to establish a relationship on linked in. That immediately gives me insight into their background, and, some clues (but no guarantees) as to their legitimacy. In particular, 95% of the time we're only two-hops away, and more than 50% of the time we know somebody in common - so I can quickly drop a line to someone I trust personally and get the inside scoop on this new associate of mine.
Anybody who is trying to use Linked In for more than a Rolodex is missing the point. It really is nothing more.
Also, (And I'm not sure if this is just me) - I have about 300 or so facebook friends, and about 400 Linked-In contacts, and, with maybe a half-dozen exceptions - there is no intersection between the two sets. I don't share pictures, wall-history, or personal updates with business colleagues, and, I have no desire to pollute my linkded in rolodex with every aunt, uncle, niece, nephew, ex-girlfriend that I've acquired in the last 10 years.