What has your experience been like with collaboration between engineering teams that work in different countries?

Having different time zones can be challenging. However, if you look at it the other way around you'll see that instead of a five day working week we have six days with engineers working almost 24 hours. With proper planning and clear and continuous communication you can get more done and ensure team members are not blocked because of the time zone difference. It is also important to be considerate and flexible.
In my experience, all the teams I worked with were very considerate and aware of my time zone. I never felt pressured to work late (since I'm in Cairo) or work on a weekend. All our meetings are scheduled in the common hours and for the Cairo team the start of the day is were we get all the work done and for the US team their focus time is the second half of the day.