My Global Technical English class has been starting with simple web 2.0 applications this year. It has gone far better than trying to integrate and teach them as needed.
this is the order I taught them in, and it seemed to work well:
5. Google Docs
Now, I know I will be doing some reteaching as we get into the practical application of these, but just having more kids already knowing how to use them will be handy.
BTW: The one the liked the best was iGoogle (no surprise), followed by delicious. The one they have struggled with the most is Docs. They did think the auto-saving was cool.