Do you think you could send me an email (in my profile here), I'd love to pick your brains about using Pharo in production!
So, load balancing and monitoring you can do with things like nginx and monit.
Of course, I am no in the league of doing the next Twitter. It may keep up tough.
I am tying everything together with RabbitMQ, so scaling is doable.
Storage for blobs etc is in Riak.
with Amber you can use also node.js if you want. And any server side node.js library you can get your hands on. Amber can use any js library.
You could even mix amber, pharo , node.js and seaside / aida-web .Sky is the limit. Its up to you which specific approach you will choose. You definitely have loads of options.
There is of course a downside: a really tiny community... took me a while to get used to the Iliad way, but I'm not going back unless Seaside shrinks to 1% of its current size and makes AJAX integration as easy as Iliad does :)
Anyway, I guess the future is not about server-side frameworks, but something like Amber + some sort of Pharo REST service (kinda like Seaside-REST) + some sort of magic persistence (kinda like Voyage).
Also put my money in there as a consortium member.
Really a great feel and awesome community.