Not as many as you might have thought. At least not according to this wonderfully informative blog post by author Jody Hedlund, detailing how Facebook uses a calculation called "EdgeRank" to determine which of our Personal account and Page posts show up on our friends' news feeds.
Here's the kicker - you can PAY to promote the post and have it appear on more feeds.
Are you surprised?
At least I finally have an explaination on why some friends' posts don't show up on my feed, but are visible if I actively search out their account. Silly me, here I just assumed I had missed their post in the never-ending flow of info.
Really, check it out. Jody has written a great post, and has including several links for those who would like to learn more.