I'm afraid time is of the essence here :). Not for all functions (i.e. switching between home- or away-temperatures on a thermostat), but one of the things the Arduino controls is a (3-color-led-) light dimmer. You control a slider in the interface and the dimmer is set accordingly. A slight delay is acceptable, but when it takes a second for the light to react it will take several tries before you reach the right mood/color. And having the Arduino poll the server every 100ms seems like overkill to me...