Don't know, but I have a mirror image point to make that's appropriate for this thread.
Since the new site, I've switched to using Invisible mode. I never minded users being able to click into my username and see when I was logged in before, or see when I was online by looking for the green button under my name. But it does bug me that if you're not Invisible on the new system, your username appears in very large bold type in the reactive tag cloud for Who's Online on the main styleforum page.
Before the change, the ability to see if someone was only was largely an active, user-driven thing i.e. if you wanted to check if someone was online, you looked at their profile or for the green button, and got the data. This was useful, but also maintained a sort of vague privacy (someone had to make an effort).
Now, it's both less usable (ie miran's point in this thread about not being able to see when they last logged on, even if they didn't post during that logon period) but there's also an intrusive/automatic forced passive breach of privacy in the outsized font used for recent logons in the Who's Online cloud.
Result? Whereas before I didn't mind people being able to check whether I was online, now I resent it being intrusively advertised, so I've used Invisible mode to hide the data completely. Classic example of the law of unintended consequences.