I'm a Linux user already. Should I use LinuxMCE's distribution
Yes, LinuxMCE is based on a standard Ubuntu distribution. We only added to it--we didn't take away. So you can still use your Core as a normal Ubuntu PC. And the additions we made can be bypassed if they get in your way, explained below. DCERouter and the other devices, like the home automation modules, all run in the background in screen sessions and won't interfere. While you could try to run LinuxMCE on your own distribution, it's not really recommended. LinuxMCE has lots of scripts and utilities to facilitate various tasks. Plus LinuxMCE embeds many other open source projects, like Xine, Asterisk, etc., with our own "wrappers" that allows them to work together seamlessly. These wrappers are only tested against the versions we maintain in our Ubuntu mirror. And before we upgrade anything on our mirror, we thoroughly test the new packages in our system to be sure it still works. Also remember you only need to install LinuxMCE's software on 1 PC to be able to use it on all the PC's in your home. The Core exposes a network boot service for every other PC so they become dual purpose--hard drive boot to use them like you do now, or net boot them to use them as media directors. So you don't need to dedicate any PC's to be media directors; only the one PC running the Core which provides this service needs to be left always running LinuxMCE's software. Here's what we changed:
LinuxMCE includes lots of scripts that automate all aspects of maintaining a Linux system. For example, when you add a new user with the LinuxMCE Admin site, it automatically creates a new media directory, exports a samba share, creates an email and voicemail accounts, and so on. There's also scripts to do lots of low-level things like setup ip network prioritizing so your VOIP calls are clear. By default, LinuxMCE overwrites and re-creates many Linux config files at each boot so LinuxMCE acts like a black box appliance. However, once you install LinuxMCE you can go to the LinuxMCE Admin web site, click "Advanced", "Boot Scripts", and disable any or all of these scripts. Then you can still maintain your LinuxMCE Core like any other Linux PC and it won't overwrite your config files.
Our Ubuntu mirror
We maintain our own mirror based on Ubuntu. The reason is that we have "wrappers" for many open source projects like Xine, Asterisk, etc., which is what makes them all work together seamlessly. Whenever updates are posted to Ubuntu's repository, we need to test the new versions to be sure the changes did not break anything in our wrappers, and that the auto-configuration scripts still work. In very rare cases, we need to make our own version of a package that replaces the one in Ubuntu. But we avoid that whenever possible, and instead will re-work our wrappers so that we can stay current with the "stock" version. Any such changes are trivial, and therefore you should see no difference between LinuxMCE's Ubuntu mirror and the official one.
The media directors use our own modified version of the Ratpoison window manager. All applications appear as full-screen, with no borders, and our Orbiter GUI becomes the XWindows desktop. This is the desired behavior in an appliance-like set-top box; we completely isolate the user from anything computer-like. However, you will likely not want this as your main desktop. So, we recommend you run 2 versions of X on separate terminals: one with LinuxMCE's window manager, and the other with your own preferred choice.
See also: Overview of the software modules