At the time of acquisiton (Dec 2010) the Bamboo stack was the only GA stack, Cedar was in beta which used buildpacks internally but custom buildpacks didn't come to 2012 https://blog.heroku.com/buildpacks
The press releases talk about them not being Safe Harbour yet but it is now much more in progress. Your data may pass through the US still at presently.
3) Tmux sessions are restricted to the size of the smallest client connected to the session. We've recently started using it at work and it works fine for 2 of us, but 2 others found that the resolution differences between their 13" and 15" macbooks means that the 13" sets the tmux session size so the 15" doesn't use the whole screen.
I'm pretty sure this would also be an issue with screen. The pair maybe able to operate on separate 'windows' at different sizes, but would not be able to view the same window at two different sizes at the same time.
Actually Screen is even worse; it sets the size to whoever joined last. So if someone with a big screen joins a session of someone with a small screen, portions of the window will be invisible to the person who started it.
If a Heroku application's DNS is setup correctly then you can usually avoid problems like this on the new Heroku stack (CEDAR). It's important to reread the documentation on using custom domains but also be VERY aware of using naked domains (mysite.com) in your application. This isn't just a Heroku problem, it's a DNS problem. Heroku have recently had a spate of routing issues (usually DDoS attacks) which would have been largely negated by correct DNS setup and either avoiding naked domains or using a DNS host that lets you cname a naked domain to a host.
Could you please elaborate on why exactly using (non-CNAMEd) "naked domains" is a problem? What do "naked domains" and DDoS attacks have to do with each other?
DNS only allows you to put an IP addresses on the apex (read: bare/naked/etc) domain A record. That means in the case of a DDoS or other problem affecting one of those IPs you run the risk of having degraded redundancy. Some people unfortunately only put one IP in, which means you're only one machine away from going offline. A long way from what you'd want from the cloud.
DNSimple have created an ALIAS record type which gets around this problem nicely, and Route 53 from Amazon takes a similar approach.
At the time of acquisiton (Dec 2010) the Bamboo stack was the only GA stack, Cedar was in beta which used buildpacks internally but custom buildpacks didn't come to 2012 https://blog.heroku.com/buildpacks