How often does Bitcoin connect to the fallback nodes? Does the standard client have a preference for connecting to fallback nodes (for example, by trying to have at least 1 connection to such node at all times), or are they treated like any other nodes?
Bitcoin only connects to them specially when you don't have enough nodes, and then it will disconnect as soon as the seednodes give you a nodelist. Bitcoin might choose to connect to seednodes as regular peers as well, but they're not given any preference.