Writing High-Availability Services?

bigattichouse asks: "I have a project coming up that will require some serious load capabilities accepting socket connections. while I have a design that can be distributed over multiple servers (using queued reads/writes to the db) and is as low-overhead as I can make it - I am concerned about falling into common problems that may have been overcome in many other projects. What strategies (threading, forks, etc) give the best capability? What common pitfalls should I avoid?"