The BIG Secret-- You're using Linux. Whether you knew it or not.

Linux Secrets
Ahhh . . . But that's the thing about Linux and other Free and Open Source Software - there areno secrets.You can have the entire source code, so there are no hidden "easter eggs" and no hidden surprises. Or are there?
The Big, Big Secret:
Look around you - if you can see devices like a personal video recorder, an ADSL modem/router, a VoIP phone, then the chances are you're using Linux, since many of these devices are powered by embedded Linux distributions. For example, in my office, I have a NetGear DG834 ADSL wifi router and Snom 320/360 IP phones, which are based on embedded Linux. The DG834 is quite "hackable" - there's a well-known trick for getting to the command prompt - so I can use Linux commands when problem-solving. The Linksys WRT54G router has been hacked to an even greater extent - there are complete replacement Linux distributions for it, offering improved features.
Many personal video recorders, such as the TiVo and theTopfield TF5000, run Linux, as do media centre devices. In many cases, these have been extended in various ways. You can even install Linux on an iPod, and do useful things with it.
That this is possible is due to the fact that Linux is open source; device developers can take the Linux kernel and cut out unnecessary subsystems, compiling it to produce a small image that will fit in the ROM. You don't need SCSI drivers? Take them out! You don't need any disk support at all? Rip it all out! And, of course, it helps that Linux has been portable across many different processors for a long time, so whether the device is based on a MIPS or Hitachi processor, you can still target it. In addition, becauseof the terms of the GNU Public Licence, if those hardware developers write driver code, they are required to release the source code, so that we can all benefit. This has worked well for all concerned - more than a few Linksys routers have been bought specifically because of their ability to run modified code.
But Linux is working for you, even when you're not using smart devices that use it internally. If your ISP provides you with an email account, the chances are your mail is delivered to and retrieved from a Linux server (or perhaps BSD, it's true). When you access popular web sites, the pages are often provided from a web accelerator operated by companies like Akamai and running on Linux. And of course, if you search the web using Google, you're using a massive cluster of Linux boxes.
So, the big secret? You're using Linux. Whether you knew it or not.