Hmmm ... from what I have read, there is a 250 link limit in a stack at delicious, so that can't be the problem. Have you asked them?
Delicious is the only bookmarking site that I actually use to do what it was intended to be for - bookmarking things that I want to access later. I find it a great place to organize websites that I will need to go to for various reasons. It is instrumental in my whole organizational process, in fact.