If you want to hook your surface up to dual monitors, then it's your only option.
I've been weighing it myself, but I only have a single monitor I connect to, and my keyboard/mouse are BT. Essentially all I'm saving myself is the time to disconnect and reconnect my display and speakers, so I'm finding it hard to justify.
Similarly, even if you needed the ethernet or more USB ports, you could always buy a USB ethernet adapter and/or a USB hub. Combined, those last two items would come in significantly cheaper than the dock.
Then again, the dock eliminates all of those cables sticking out of your beautiful surface - can we put a price on aesthetics and convenience?