My company, UG-WebDesign, uses Mandrake Linux. I use Mandrake for the Web Server that runs our primary site along with several of our Clients sites. In addition, I also setup Mandrake Linux to run as our internal E-mail server.
The setup we are currently using is Mandrake Linux 9.0 running MySQL 3.23.52, Apache 1.3.26, and PHP 4.2.3. Along with the we are running Postfix and the IMAP server for our internal E-mail.
We originally started with Mandrake Linux 8.0, but tried several competing solutions including FreeBSD 4.7, RedHat 7.2, RedHat 8.0, and Windows XP Professional. For our needs, we finally decided to return to Mandrake Linux as the best of choice. With this, we gave Mandrake Linux 9.0 a try and haven't looked back since. Our main reasons were that Mandrake Linux was the fastest, most stable option for us as our Hardware is slightly aged. We see minimal slow-downs even with steady work loads. This is especially noticeable when comparing Mandrake Linux to the Windows XP server we tested. The Windows XP server couldn't handle more than a few simultaneous connections before seriously beginning to slow down the entire network.
We will continue to use Mandrake Linux 9.0. At least until the next Mandrake release. :)