We use the Enterprise version running on a Solaris for our production server. It took a couple of installs to get it tweaked just right. My suggestion is to understand all the of services that you will be using before install i.e. smtp, LDAP(iPlanet is the only one they "technically" support), hardware monitoring, FTP, cluster etc. Most of this is allreay part of IIS and NT operating system, but will have to be installed for the Linux box seperatly.
For security and reliability alone I highly recommend running it on a Linux/Solaris box. My only question is do you have an EXPERIENCED Linux admin that can maintain it? If you are unsure about this..then I would stick with what you currently using.
Our experience has been great since we went live with it. We have not suffered any downtime at all. With the extra time that we spent setting it up, it has been great to work with. It requires little maintaince outside of clear logs every now and then and changing out tapes for backups.
hope that helps,
jgroove