Jeff Pulver has always been the consummate networker. People want to know him, and he's the type of gracious and wonderful individual who makes time for others. So, it's easy to understand why Jeff feels a need to disengage himself from the LinkedIn introductions process. When people you don't know ask for introductions to your friends, you want to know whether the introduction is going to be received well, and you want to know a little about the individual you are introducing.
I'm personally a user of LinkedIn, and connected to over 1500 people, some of whom I don't know very well. It's a direct contradiction, by the way, of what LinkedIn advises you to do, which is to only link with people you know and would recommend. Why so many? LinkedIn is an inexpensive recruiting tool, which has provided high quality candidates in the past. Compared to monster.ca (the previous job posting site I used) LinkedIn is dramatically cheaper, and produces a much higher percentage of quality candidates. By having a large LinkedIn network, I have access to more candidates. What that means, though, is that I am a little more discriminating about who I will introduce and who not.
Kfir Pravda has written a fun follow-on to Jeff's posting, in which he categorizes social network users.