Ask HN: Best solution for a user-customisable site

I'm working on a project which will hopefully allow users to customise their site (hosted by me) as much as possible i.e. change the colour scheme etc.

I want to make the options as user friendly as possible for non-techies but also as flexible as possible meaning column width and page layout etc. are editable too.

Any suggestions for great examples of where this has been done successfully? I've looked at a number of site including SquareSpace which I think balance this process relatively neatly.

I'm using rails so if anyone can suggest any project tackling a similar issue that would also be great but not essential, just examples of an effective customisable interface would be really useful.

Cheers!