I immediately thought that this guy had done a very good job of domain name selection. The name was easy to remember. It had keywords in it, including one that was geo-specific. It was also perfectly descriptive of the medium on which it was displayed: the van itself! And that van was bright orange, making it really eye-catching.
If you look at the drop down menu in Google you'll see that "Perth cofee van" comes up as a suggestion. Now is that because lots of people have seen the van, and so type that as a query? Or is it because it's something that people want to find anyway? Either way, being on the very top of the results the site is sure to get regular, quality Google traffic. (Then there's the "type in" traffic from people who have seen the van and clearly remembered the URL. With the van being seen by thousands of people a day it would have to draw a small but constant flow of local visitors this way.)
Now it's interesting that he's chosen to do this because the actual business name is Coffee Crusader. Maybe they've got a fleet of vans, and each targets slightly different keywords in the individual domain name?
In any case the business owners have clearly thought about this particular domain name as part of an overall strategy. They also really know how to stand out visually, which is just a good general offline tactic anyway. Their approach is a good illustration of how effective a domain name can be if it is memorable, descriptive and totally appropriate for the medium.