I'm familiar with some of the strengths of Erlang, but the slides look like they're written from the point of view of someone that likes Erlang and was looking for a way to justify rewriting Delicious in it, rather than explaining what about Delicious made Erlang a wise choice for the task.

someone that likes Erlang ... what made Erlang a wise choice for the task

You've just answered your own question. You can solve every problem in every programming language -- as long as you like what you're doing. If you pick a langauge you like and a project you like, it will probably get done.