Heroku for Facebook Developers
heroku.com
heroku.com
I don't doubt these are the resources necessary for a 1M user site and I don't even doubt that that's a good deal for not having to manage a site of such scale, but how many people are $1500/month ready to test an idea?
Also, support is extremely important for these big campaigns. Companies want someone to call if things go awry. If Heroku goes down, you're kinda screwed. All we can tell the client is "sorry, Heroku's down. we can't do anything about that." That's something you want to avoid.
For the ones that go big, they go big fast!
When we started out our business in 2008, we needed to double our capacity every week for 6 weeks. I spent a lot of time adding servers and moving providers as our old one couldn't move fast enough.
Personally I would go for an AWS Free Tier account + 1 EC2 large instance. Then use the micro instance as the HTTP server, and the large instance for the DB and a 1 GB memcached.
That would cost no more than $100 / month and will give you more processing power than what this package offers.