Does anyone know if there's a way to use Netflix when PSN is down (which seems like a fair amount of time these days)? I've no idea why you need to be signed in to use the service in the first place, but I can't seem to find a way around it. Many thanks.
No. You need to be signed in because the console effectively doesn't have a network without it; all traffic is routed through the PSN service, so no PSN, no traffic.
Definitely one of the downfalls of the PSN, but XBOX Live behaves similarly. I think the general plan was that PSN won't be down unless updating, but obviously this isn't working out too well.
Another major downside is that in 20 years when they finally take down PSN/Live servers you'll lose half the functionality of your console. Of course it's 30+ years old now and you're lucky if it's even running, but still.