My least-proficient users are still able to perform their basic functions in Salesforce, namely monitoring accounts and contacts, creating and updating opportunities, and logging calls or emails. Because many of their day-to-day processes can be automated, at least in part, by the CRM, it makes it more user-friendly, even for those who still prefer to use paper and pen. Similarly, my super users enjoy the vast reporting capabilities available to them, and they understand and appreciate the kind of customization we can do to the system. Having a central, powerful CRM like Salesforce helps them stay focused, and they bring some great ideas my way that can help us improve the usability even more.
The one draw back is that sometimes too much choice can paralyze, and I see at times that my less active users are often those that come to me wondering whether A or B is the better way to do something. They can become confused as to whether to use a report or dashboard and, if a report, which fields to sort by, etc.