I've been using FreeBSD for years now (everything from my first 486 apache web server w/ 16mb of RAM to a compaq proliant quad processor server w/ 4gb of RAM) and 6.1 definetely doesn't let the product line down. I wouldn't run anything mission critical on any other OS.
Personal Uses:

Web server

DNS server

Database server

IRC server

Mail server

LAN Party server

There are also a ton of great howto articles written for completing certain tasks. While its shortfalls might be in the desktop area, you can't really compare a Server OS to a Desktop OS can you. If anyone ever wants advice on building an infrastructure around a Solid OS, I can't imagine why it wouldn't be this one.

My own personal opinion is that this is a great release for a great operating system. But I have been known to be biased at times. I think the best review came from my step-mother.

Long ago I converted her computer to FreeBSD for various reasons. One of which was that she wanted to try it out -- even though she is computer illiterate. I am able to maintain and upgrade it from my house and without her even knowing about it. Which is fantastic and one reason that command line system administration is the way to go if possible.

Anyway, a month ago her hard drive failed. My father quickly swapped it for a new drive and threw "another" OS on it. This was the middle of the week so my father told her not to bother me until the weekend. But within 24 hours she was on the phone begging me to put FreeBSD back on her computer.

She had just gotten so used to it "just working" that the change was too much for her. And, as horrible as it is for a user to be unable to adapt, that speaks loads for the stability and consistent nature of the OS. It has been upgraded through several revisions (even major versions) and she was still able to get used to a consistent environment.

Note: she did get it back (and all her files too) and is happy as a clam now. The only problem I have is that she's become a vocal advocate for it and is trying to convert her friends and I'm not interested in supporting them through the initial learning curve.