Shane,
Many ways. Keep in mind there are two-sides to this coin. Customer Satisfaction and Customer Dissatisfaction. Both measures are important.
Two type of information can be obtained, inbound and outbound. Outbound is when your organization sends out a survey (questionaire) to gather the Voice of the Customer. Inbound data is obtained through Customer Reporting, inbound calls (unsolicited), anything that comes in without you doing anything. Generally speaking, complaints air high on this list, as you will often hear when you are doing poorly, rarely when you do things right. Both types of information is useful and important.
You mentioned visits, another form of outbound information gathering. Perhaps the best. With face to face meetings, you are able to develop better information. For instance, if you have a questionaire scaled 1 to 5, 5 being the best, you may receive a 3. The 3 becomes a hard number. You can not ask why (unless you make a follow-up call) while in a face to face meeting, you may ask/challenge the rating. You may determine that the 3 was in fact a 4, but rated only a 3 because of your "latest great mistake". Face to face, you can get a more objective answer.
Got to run to a meeting, so I'll turn it over to the group. If you have the means, you may want to look into an ASQ sponsored training event called 'Measuring and Managing Customer Satisfaction and Loyalty" to be held again in June 8-10 in Raleigh/Durham, NC. The cost is about $1000 per attendee, and is a good introduction to intermediate overview of concepts and techniques.
Regards,
Kevin