Probably several hundred... at some point you cross your own personal line of comfort regarding the work it requires to replace a dead hub. I haven't heard of them dying.. but I suppose it can happen. No moving parts but it's not impossible.
If I had 150 devices on a single hub, I would be having that conversation in my head about just how long will it take to re-join all those devices to the replacement hub? If I cut that in half, 75 devices across two hubs and it's certainly a lot more comfortable a task.
Another way of looking at it is, perhaps... how much $$ is invested in devices and at what point does the extra cost of a hub become "small potatoes"?
My 'point' was at around 65 devices that needed to be migrated off the original hub and onto a new one. And if the hub is on sale, like it is through this weekend only, then is the 'point' is even lower?
Lol, some of you guys whining about the price or 10 bucks here or there. I just bought one from Asia and it cost me nearly 180 bucks including shipping and import duty. That's how much I wanted this device. And now I wish I'd bought two because I find it's excellent and so I need another one for a 2nd property. Time to get my wallet out again!