If you still think that everyone who blogs is a member of the same community, check out Buzzmetrics Top 10 Most Linked To Blog Posts of 2006.
The top post has 800 or so links in, and it is a petition in the LiveJournal community not to change the interface.
800...and then they really drop off from there.
So basically, in a community of 60+ million blogs, according to Technorati, no more than 0.00126% of people linked to the same post at once.
Of course, that doesn't count del.icio.us tags, where sometimes posts get a thousand links or two, but even that's just a drop in the bucket.
Even the most popular blogs overall don't have significant mind or market share when you think about the overall blogging audience, let alone the readership. Engadget and Boing Boing have about 20,000 blogs linking in... or about 0.033% of all blogs.
So, before you think that pitching to the most popular blogs overall is going to make or break your product, get a little perspective. What is the right audience for what you're trying to do? Maybe you're better off pitching to a recipe blog that has 200 really active readers versus a tech blog with a hundred thousand readers who mostly just browse and comment to be seen.