Now I see why people might be asking to hide their listening data. File-sharing, downloading albums leaked early and potential legal consequences thereof. Now I'm interested. Will Last.fm protect them? Maybe not now but if there's enough pressure from listeners, in the future?

Why would last.fm protect people who are breaking the law and harming the interests of the companies who provide much of the music for the site?

And if you don't want people to know you're listening to leaks, either don't listen to them in the first place, or simply turn scrobbling off when you do.

About the filesharing thing: I think that is a non-excuse. Personnaly I don't give a rats ass about the RIAA. I live in the Netherlands, and my country's laws allow me to download and listen to all I can get my hands on. In here you get trouble for uploading, and Last.fm does not have a counter that shows the amount of gigabytes one has uploaded through the various routes. If it is filesharing-issues that alarm you, you better leave all the groups that are connected to one of these programs instead of worrying about unreleased tracks showing up on your (possibly) private tracks.
The "Last seen" can be circumvented by not visiting your profile. The time mentioned there is just that. The last time you looked at your own profile-page.

Blocking people from viewing your profile would only work if it was impossible to view profiles when not logged-in (otherwise they could just log out and view it). It'd also be possible to just create a second account and view it from that.

The situation you've just described is a problem which goes far beyond last.fm, and not really one which I feel should fall to last.fm to deal with.

This whole "private profile" thing isn't what it supposed to be, it's not called the SOCIAL music revolution for nothing!

Like many said, disable recently listened to tracks is the best you can do. Otherwise, disable scrobbling when you want to listen to stuff not to be seen on the profile.

This place isn't going to be turned into Myspace for the privacy freaks, just remember that.

*votes NO for the suggestion*

This whole internet privacy issue has gone overboard. I can get setting privacy options on social network sites such as MySpace, especially for those who are underage, are only there to share pictures with people they know in real life, have been stalked, etc. (The list is endless, really) But it seems to be a virus that's spreading to ridiculous proportions. I personally could care less if someone can see the last song I listened to. How does this invade my privacy or harm me in the slightest? If it does bother you, just turn that feature off. Last.fm can not work nearly as efficiently with actual recommendations of networking, etc., if people just opt to close their profiles down to just a few splattering of people. If the idea of people on the internet seeing the music you like horrifies someone so badly, they should use Last.fm to browse but not scrobble.

I don't understand why people would want to hide their profile?
It's not like facebook or myspace where you write about your interests & have lots of pictures. You have one picture which doesn't have to be a picture of you, you don't have to write in your gender, age, or location or anything like your interests, it's all optional. I think being able to set your profile to private would be pointless.

There's times where people come across your profile & want to add you because of the music you listen to, sharing the same music taste. If it's private nobody will be able to see. I understand if people don't want strangers adding them on last fm, but they can just simply deny the friend request. Sorted.