Just released on GotDotNet: MacawSharePointSkinner, a server HttpModule that allows you to modify the look and feel of SharePoint sites without having to change the core site layout. (found via Mark Harrison) You should also be able to use it to modify non-SharePoint ASP.NET web sites. It looks very promising for certain situations (probably not all - as my friend commented, why would you want to do customization work and then change your changes? Plus ASP.NET 2.0 will include skinning right in the package). Where SharePoint is involved, however, this could be useful since certain customizations can be quite a bit of redundant work.

From the MacawSharePointSkinner documentation:

MacawSharePointSkinner is a tool designed to enable non-intrusive modifications to the visual and functional design of SharePoint. The tool can be used for both Windows SharePoint Services 2.0 and for Microsoft Office SharePoint Portal Server 2003. Actually, it can be used for any web site utilizing the ASP.NET technology.

One of the major issues that we encounter in the implementation of SharePoint within organizations is that organizations want modifications to the visual and functional design that are almost impossible to implement without a major overhaul of the standard files and templates provided with SharePoint. SharePoint is constructed as a kind of standard product that is best used out of the box. Some design can be applied by specifying themes (for team sites) or by modifying CSS stylesheets (for the portal). The possibilities here are limited however, and changes to the actual HTML that is rendered results in changes to hundreds of the standard files.

When implementing customer requested visual modifications, one of the big problems that we encountered in making extensive modifications to the files and templates delivered with SharePoint was that the rendering of the same HTML is implemented differently by different pages. Some pages contain the actual HTML that is outputted and can be easily modified. Other pages contain server controls that do the rendering of the same HTML. These pages are almost impossible to modify. Another problem is that modifications must often be made to hundreds of pages.

The approach that MacawSharePointSkinner takes is that it lets SharePoint render the final HTML, and just before this HTML is sent to the browser MacawSharePointSkinner makes the needed modifications to this HTML. This is done in such a way that no modifications are needed to the internal files of SharePoint, so it is non-intrusive. Another advantage is that it will survive service packs (although the output HTML may change in a service pack!) and template modifications.

Interesting. Get it here. If anyone makes any screenshots of interesting implemetations of this, I would be interested in seeing them.