As per our discussion at the conference, about maximising our skin optins by sharing CSS classes with another project, I have looked into both the UPortal CSS and the OSWD. UPortal seems to put 'UPortal' into its class titles which makes using them a less attractive option. OSWD doesn't work from one CSS, so that wouldn't provide any advantages. I also took a look at Plone, and it looks like this maybe a better option. Plone has many skins and the CSS validates and doesn't use "Plone" in the class names, so it may be worth trying to match up with that one. I'll look into it further.
