Gav, is it possible for users to choose their theme in the user preferences (like some other forum systems).
Yes it is possible, but for the sake of simplicity I'd rather keep it to 1 theme. I'm going to go with a relative width, so it will adjust based on screen size. The problem with wide forum layouts is that large chunks of text become difficult to read due to the very long lines of text. For readability its best to have 12-16 words per line.
Also since I've been given a Nexus One Phone and I use it to check the site frequently I noticed that having a fixed width layout is a bit of a pain.
What's the main reason people want the wider ratio? Is it so large images fit? I'm just trying to keep consistency in site navigation and feel throughout all pages of the site.