I typically interact with X-many OSes per day:

Windows XP (directly) at work

UNIX (remotely) at work

Windows 7 at home

Android on my phone

OSX on my wife's laptop

BREW or whatever it is now on my wife's phone

And who-knows-what on the ATM's, cash registers, and other computers-we-barely-see-anymore which I run into every day.

So, surprisingly many. And I'm sure I've missed a few. I wonder what the CISCO VOIP office phone next to me is running...

I assume you are trolling, but I will indulge you.

Linux != cheap. Linux == Free.

As a Unix guy I think OSX is a lot like Unix in the following ways.

* It is over priced for what it does.
* Support is generally good if you pay for it, though it is not inexpensive.
* It is generally picky about what sort of hard it runs on. Often you don't upgrade a machine, you buy a new one.
* The people who are proponent of it will seriously not STFU about it.

It's not uncommon, around the house, for me to answer her cell phone if the kids have her occupied (or vice versa). And I'll often use her laptop for just a moment to check a map, a calendar, or a webcomic, as my home computer is a gaming rig in the basement.

And, of course, there is the ever present "providing-tech-support-to-family" angle, which covers both laptop and phone.

Do you drive a car? that's another OS.
Phone? Another OS.
How about your TV? That runs Linux. (Yes it really does, look at your manual.)

If you are a windows user, that is 4 for every person that owns a car and a LCD or Plasma TV.

I ride a Motorcycle and have 3 cars, so I interact with 7 Operating Systems every day.

Oops, forgot that the Copier here at work Runs QNX, That's 8.

The question behind "depending" goes even further. Off the top of my head:

iOS 5 on iPhone / iPad / AppleTV 2
Mac OS X 10.7 on MacBook Air
Mac OS X 10.8 DP3 on Mac Pro test box
Windows 7 SP1 on Lenovo x220
??? on BMW iDrive controller in my car
FreeBSD on NAS device
various servers on the Internet (Windows, UNIX, Linux, etc.)
various embedded OS versions on consumer electronics devices (HDTV, digital receiver, etc.)

The world runs on software, whether you know it or not.

If you interact regularly with an ATM, then your answer should probably also include OS/2.

I don't count Android as a distribution because you can't change any of the parts yourself, especially the kernel. Unless you hook up your phone to a debugger, you can't do anything at all with the guts. I consider it based on linux the way OSX was based on BSD.