I'm not sure if this is really any worse than the things Facebook does intentionally (i.e. change default settings) to erode privacy, except that this one seems like an unintentional bug exposing status updates to people you're not connected to.
I recently noticed some updates in my newsfeed from a high-school friend that I didn't remember connecting with. Let's call here Selena. When I click on Selena's profile, it turns out that I am not friends with her on Facebook. However, I had sent her a friend request several months ago that she never accepted. She has clearly set her own privacy settings to be stricter than Facebook defaults because I can see almost nothing except her name and picture on her profile page. Well, that and the fact that my friend request is "Awaiting Confirmation."
I don't take it personally that she never accepted my request - maybe she doesn't remember me 20 years later. However, I can't help feeling awkward at best and voyeuristic at worst now every time I see "Selena is now friends with So-and-So," and "Selena has joined the group Such-and-such" scrolling across my Page.
I recently also started pruning my friends list of people I had added just for games like Mafia Wars. Again, nothing personal - I don't play much Mafia Wars anymore. Yet, I was unable to remove at least one friend from Mafia Friends list because she never accepted my request to begin with. Let's call her Default Donna. I see Default Donna's Mafia Wars updates all the time, and assumed we were legitimately connected until I realized I couldn't remove her because we're not really friends. Here I am the creepy voyeur again.
Facebook: Please let me remove people from my newsfeed whose updates I know I should not be seeing. I'm not like that.
This appears to be a bug related to the Lists feature on Facebook. When I sent the request to Selena, I added her to a "High School Friends" list. When I sent the add-me request to Default Donna, I added her to a "Mafia Wars Friends" list. Their updates DO NOT show up in my regular newsfeed, or "Most Recent." However, I usually view my newsfeed using list filters. When I click on the High School Friends filter, there is Selena all over the place. When I click on my Mafia Wars Friends filter, there is Default Donna all over the place.
The worst part is I am not entirely sure whether this is a bug or feature. Facebook is very opaque about how it decides which posts to include in your newsfeed, and it seems deliberately confusing about what privacy settings control. Whether it's by design or not though, it should be considered a significant privacy violation.