I'll take a shot at it.
First, Linux is a kernel -- not an OS -- that Red Hat combines with other software they choose to form the production Red Hat distribution of Linux, currently Red Hat 7.3. As you no doubt are aware, there are hundreds of distributions of Linux. With FreeBSD, there is only one "official" production version of FreeBSD (right now version 4.6). Many would say that with the BSDs one has a complete operating system...with Linux, you have a kernel anybody can use to roll their own operating system. In fact, there is a Linux distribution called Linux From Scratch that guides you in doing just that -- rolling your own Linux "distro" from scratch.
I've asked about the merits of FreeBSD .vs Linux at a few places online. The consensus of what I've been told by those with more experience than me (I'm still new to *nix, but learning) is:
1) FreeBSD is regarded as better for a webserver OS. IMO, folks regard FreeBSD as more stable, having less downtime, easier to keep upgraded via the FreeBSD ports system, and not to have as many security holes over time come to light for it as come to light for Red Hat Linux.
2) Red Hat Linux in particular, and Linux in general have much more hype and mindshare going for them than FreeBSD. This means if you need an OS to have the latest software drivers for hardware, you are more likely to have that with Linux than with FreeBSD. This is important for gamers in particular. With either OS, one needs to be aware that not all hardware is supported by Linux or FreeBSD. For most, the best option is to download a free ISO image from the internet, burn to CD and see if it installs OK. If not, figure out what hardware you need to replace, and decide if it's worth the money to you.....or if another flavor of *nix, such as Mandrake Linux, might work better.
3) People regard FreeBSD to *be* a Unix operating system, whereas any Linux distribution is a "Unix-like" OS, rather than a Unix proper. One of the major things people point to is the directory structure of FreeBSD being more "right" in a Unix-ish way than Red Hat's directory and file structure, which may change with each distribution. People find the more logical to their Unix thinking minds file layout of FreeBSD to help with system maintenence over the file layout of Red Hat Linux. Many Linux advocates regard Slackware Linux to be the most Unix-like Linux distribution.
4) There are fundamental differences in how each of the two operating systems do things "under the hood" that one can learn about to one's hearts content online, but is not worth going into here...and I'm not knowledgeable enough to be either OS's spokeperson in this regard.
5) There are differences in how various commands and utility programs work under both OSs...but they are still both Unix-ish and more similar to each other than either one is to windows. Learn one, and you know most of what you need to be functional with the other one, IMO.
6) Both operating systems have their strong supporters that sing the praises of their chosen OS and bash anyone preferring the other OS.
7) There is more information online and geared to *nix newbies for Linux in general, and Red Hat Linux in particular than exist for FreeBSD. However, some would say the online and print documentation for FreeBSD is superior in quality to that available for Linux -- and is totally adequate, too.
When FreeBSD 5.0 (and early 5.X point releases) comes out over the next year or so, the hype meter (and resulting reference material) will likely sway a bit more towards FreeBSD from where it is now compared to Linux. Both these two operating systems are likely to get better and better with each passing year.
8) As with most things technical, the answer of which one is "best" is....as usual...."it depends". It depends on what your purposes are. If I wanted to dive into the world of unix from a Windows background by loading one or the other OS on a personal computer at home to see what all the *nix fuss is about, Red Hat Linux would be an excellent choice. There are many GUI tools to help when just starting out with most Linux distributions (Mandrake is an excellent example....and choice for newbies, too).
To me, an ideal setup (and what I have on my desk) is a computer with multiple hard drives, each with it's own operating system. I use a Romtec TRIOS hard drive selector ($50) to switch between three hard drives. On my system, one hard drive has Windows 2000 Professional, one has Linux and the third hard drive has FreeBSD on it. I hit a button to select which hard drive (and OS) I want to boot from, then power up. The TRIOS locks out the other two hard drives. So no matter how I might trash a hard drive as I learn *nix, the other two hard drive cannot be affected. I simply power down, hit a button to select one of the other two hard drives in my system and boot up into that OS. I do have a Lian-Li PC-70 case with six 5 1/4 inch external drive bays that makes the above setup easy. If I were limited to two hard drives, I would buy the Nicklock hard drive selector for $20-25 (try tigerdirect.com and note you may need to also get the 3 1/2 to 5 1/4 drive bay adapter depending on your setup).
One can also multiboot, but if you trash your hard drive while learning, you've trashed all the operating systems on that hard drive...which may have taken you several hours to install. I like limiting my "collateral damage" from learning to one OS on one hard drive. Also, how best to partition a hard drive is a part of what one learns as one learns *nix; another reason I prefer multiple hard drives.
There is also VMware (about $300), where you can have as many operating systems as you have hard drive space and memory for not only installed on one hard drive, but also booted up and running at the same time in their own separate virtual machines. This is especially good when you want to learn networking between the various operating systems you currently have booted up under VMware, or benefit from the rapid speed you can switch between concurrently running operating systems, such as when testing various versions of browsers (think different versions of IE under Windows) -- each one on a different OS. Note you need a separate license for each version of Windows installed under VMware; if you have three versions of Windows installed, you need three Windows licenses to be legal.
Moreover, if I wanted to set up the most reliable, secure and trouble free public web or other internet type server I could on an Intel rackmount server box, I would choose FreeBSD. If I had to choose a Linux distribution for a server, I would check out Debian or Slackware Linux....but only after I had gained familiarity with Linux via the Red Hat or Mandrake distribution.
There are many more differences that the fan base of each OS might chime in and mention. But the above is what comes to mind before I head off to bed.
Hope the above helps.