In case you missed it, Delicious have announced that:
We plan to take the system offline this Wednesday, 19 Oct, from 10 PM to 2 AM PST in order to update our data tier and make some improvements to our search infrastructure.
I am assuming that this means that the site and the API’s will be inaccessible for those four hours. Practically speaking, this means that you won’t be able to sync Yummy.
However, adding, editing and deleting of bookmarks in Yummy will continue to work and any changes you make should sync back to Delicious when they’re back online.