Site's design is looking really good!
I surfed in the site and wrote some notes, tell me what you think:
As the features of LinuxMCE are the most important thing when choosing it over other media centers, I think that they should be on the front page. Hence, put:
in the front page in the slideshow area. Slide for each feature, contains the text from their feature page and some image.
Since LinuxMCE requires actually an OS installation, the download page should contain links for downloading LinuxMCE and link to a detailed installation instructions page. IFrame with the wiki inside is tedious and should be avoided (IMHO).
I think that the download page should contain download links and instructions for stable releases only. It is possible to add a link in the bottom which links to the wiki where all testing releases are documented.
It should be clear for people come to the site what LinuxMCE is, what it does, and how to download and install.
System Requirements should also be in the website with a page of their own, so one can find them fast (through the upper menu).
And, what about the developers area. It lakes very important data. Maybe it should include a brief review of the development aspects and link to the wiki for more information on how to offer help in the development process.