Unless the wall is cooling his computer to near zero temperatures, I don't think condensation is going to be a problem.
Do you use your Macbook while it's sitting next to the cold wall? If so, then there's a positive and negative aspect to it. The positive is that computer equipment works best when it's cold. However, the LCD screen works best at room temperature as cool temperatures can cause delays in the refresh rate. This could potentially lead to damage over time. However, this is all a moot point if the temperature drop isn't that significant.
Exactly how cold does the laptop get? Is it like a ten to twenty degree drop from room temperature, or is it as cold as ice?