Why don't JW's wash each others feet. Their excuse is that we don't walk with sandals on dusty roads anymore. But that misses the point of instituting a ritual. A ritual is intended to be repeated so that the lesson becomes more than just a nice thought blazing through the brain.
The thing is, many people (not just JWs) do not read this text as Jesus instituting a ritual, but as his providing an example of humble service that might be expressed differently in different circumstances. In a desert environment where people wear sandals, it might be expressed as washing of feet. In modern society, it might appear as offering a cold drink or coffee or tea to someone who comes to your home. Or, perhaps, helping out a poor or homeless person with a meal. What Jesus was saying his disciples should do for each other is not the specific act of foot-washing, but the attitude of service to others at the cost of one's own convenience.
That said, like villagegirl, I have attended a Seventh-day Adventist church and participated in their foot-washing ceremony, and found it to be very meaningful. What surprised me was that it was not so difficult or humbling to wash the feet of another person. What was really tough was sitting there and allowing someone else to wash my feet. That was where I really needed to bring up some personal humility, and it made Peter's response to Jesus (John 13:6-9) much more real to me. So I have no issue with churches that choose to practice foot-washing in a literal way, but I don't believe that Jesus' words require such a literal application.