Scott, you're right 2%.
To start with, Wikipedia has a nice list of potential problems: http://en.wikipedia.org/wiki/Electronic_commerce#Problems
Considering the topic, I would add these following problems (which have have been experienced by *some* Yahoo customers as well as others):
1. problems with advertising metrics "click fraud" (and billing accordingly),
2. billing nightmares (repeated attempts to cancel service --took a year),
3. problems with domain handling
4. search engine indexing issues
