It would be nice if you could add a feature, configurable or not, that would send keep-alive messages in the background. Currently if I have a window that is inactive for a period of time, it becomes unusable. Putty for example has this feature. My ubuntu linux box at work, the default terminal just stays active. I didn't have to configure anything. It would be nice if this would just be the default behavior. Putty you have to remember to set it, which can sometimes be a pain.
iTerm is no longer under development. Please visit iterm2.com for support.
Also, this is something that should be done by ssh, not the terminal, as it would interfere with normal operations.