Moving outside our web-site
It's always interesting at conferences like Museums & The Web how individuals seem to be independently moving the in the same direction. Dafydd mentioned the Brooklyn Museum's Graffiti Mural which is a really nice example of how gallery spaces and online spaces can be combined to provide an experience for everybody.
There's also a distinction developing between a museum's web-site and a museum's online presence. In the past, if you spread your wings outside your own site, it was to pay a tourism or web-links site to promote your museum, and I think it was mostly a fruitless venture. A lot of the teams here have actively participating on a new generation of participatory sites like MySpace, Facebook, Flickr, Digg, YouTube and the community of museum bloggers (the 'blog-o-sphere'). The audience for these sites tends to be a little different to the average web-site visitor looking for opening times or driving directions.
Actively participating in online communities - leaving comments, flagging up related links, and linking to others - can be one of the big drivers for people to come to your site. If you can get this community talking to the people standing in the exhibitions, you can build a much stronger community than museums have ever had before, and reach a wider variety of people too.