AD forest binding & privacy
Hi there! I run a small Mac group at our office, so here's my take:
While your computer is bound to the Active Directory, like you said - all of your folders in your "home" on your Mac aren't being advertised (or, at least, they probably aren't) on same network. An administrator would need to either access your account via Remote Access (Apple's application for observing and controlling computers remotely), via the terminal (ssh), or similar. They'd need to actively access your computer to look at your files, and as others had mentioned there really isn't any desire on the admin's account to do so unless there's suspicion of some sort of virus/hacking or they're providing some sort of troubleshooting with you at the same time.
From an admin's point of view, your computer should only have work-related material on it. This is so in case anything goes up in smoke, all that's lost is business data and nothing of personal importance to you. Especially if it's a laptop. In the PC world, this is also to prevent the spread of viruses, as they have no idea what your home computer/network's protection is like, or the stuff you may be downloading in your personal interest (internet greeting cards, etc)
By "should", that means "rarely enforced" - personally, I don't care if you have photos of your kids, soccer practice schedules or what have you on your computer. Pirating of music, illegal content, porn, etc. I'd care about - and we have had that problem before, and usually we don't find out about it until that person quits/is fired - but mostly we care about what's on the server shares.
If you really want to keep your documents away from the possibly prying eyes of your admins, buy yourself a small external hard drive or USB flash memory device to keep your files on. That way you can access them when you want and take it home with you, and if you suspect your system's been looked at just unplug the device. Some offices may have policies in regards to bringing in removable storage (for security reasons), so check with your IT department first. However, that'd be the most effective way to ensure your privacy while not causing havoc with the IT department who'll wonder why all the directory access settings have changed.