Airport express + Belkin router = guaranteed dropouts
I'm posting this as it might help others with their airport express dropouts and frustrations. I had a Belkin N300 router 4 airport expresses (2 x G, 2 x N) which were continually dropping out after a few minutes. Sometimes they would last a couple of hours. I've been messing around regularly for several months trying to fix this, reading forums and comments with the same frustrating outcomes....
Sometimes one would disappear and reappear when another dropped out. They disappear from bonjour and airport utility when they drop out, but you can still ping them or connect through airport utility (using configure other). So it means it is a bonjour issue.
I have windows7, plus an ipad and iphone. This issue happened with all of them, so it isn't caused by windows incompatability.
I tried different wireless connection combinations (join network, extend network (which doesn't work with none apple routers) WDS (Belkin doesn't support WDS) clone my wireless network details (through create a new network) and nothing resolved it. So I moved onto lan connections instead of wireless - plugged one express directly into the router with a lan cable, and bought homeplug powerlines to extend the lan for the other expresses, completely circumventing any wireless issues that might have been happening (interference, weak signal etc).
They still had the dropouts, except the express plugged into the router lasted a little longer. So it's not a wireless issue.
I also use Rogue Ameoba's airfoil to transmit audio from other apps (firefox etc) not just iTunes, so it's not an iTunes issue.
I then bought an airport extreme and instantly the problems have gone. Perfect connections, every time. always. no dropouts. ever.
it's an expensive "solution" which some people may not say is a real solution, but at least it works.
So it is a router issue. Belkin have comfirmed they don't have full bonjour support (dated Feb 2012) and are "working on it".
Other router manufacturers may have the same issues.