I have a few brief comments then I'll STFU and let the community work on this. I never was a big del.icio.us user. But I am familiar with the problems that the community will face in a general way. 

Here are the priorities in preserving what was created by the users. 

1. As Stephen Jones says on Twitter, the data. Years worth of links and collections. The most important thing, but not the only important thing. 

2. The domain. If the community is to survive, there needs to be something at del.icio.us (and delicious.com). Ideally it would be more or less exactly what's at the Yahoo site now.  

3. The API. For apps that were developed to work with del.icio.us, preserving the API is important. 

However, one more thing, if the activity of doing what del.icio.us does is to continue and to grow, don't make the same mistake again. Find a way to host your data in a place where you're seen as a customer, where there is a sufficient revenue flow to keep it operating.