A lot of people are getting up in arms over this anonymous tell all article about the kind of insight Facebook has into your browsing habits, messaging history, and more.
I can tell you that nothing, nothing, in that article made my eyes pop out of my head or my anger rise to boiling levels. They aren't doing anything that users haven't explicitly agreed to.
- Tracking profiles you visit
Of course they do this. So does every single website you ever visit that is worth its salt. It's called web analytics. We not only can (and do) track what pages you've been to, but we also track the paths you take to get from A to B to C and so on. This is an industry standard since the invention of cookies.
- Storing snapshots of data
This is called making backups. It's a smart thing to do. How many of you very active users of Facebook have your pictures elsewhere? How about all those status updates? Friend connections? Notes? If Facebook lost all the running data, you'd probably be up in arms over the fact that they couldn't recover your data -- so backups are essential.
- Global Login
This is, again, a standard industry practice. Support engineers and technical staff always have need for this. Perhaps to verify a bug that just your account is experiencing or to diagnose some other problem specific to your instance. There's always the off chance that people (as this employee even admitted to) use it for invasive purposes, but that's generally not the goal. Also, you should take solace in the fact that Facebook seems to take this very seriously and even fires people when abuse is discovered.
What it boils down to is that you have no real privacy on Facebook -- but this is not news. And if it is news to you, welcome to every website you visit and have an account at (and some you don't...) Twitter knows who you visit and tracks you. Flickr support reps can login as you and see all your photos. Google probably knows you better than you do: email habits, favorite websites, calendar events, uploaded documents, and way more!