Somebody put it well on the tor-talk mailing list today:
"both the client and the hidden service establish a three hop circuit to the same tor relay, where the connections are joint, so hidden services will have even double the delay of normal tor traffic. If relays were homogeneous distributed among the globe, two random relays will be 1/4 earth circumference apart on average. This means that a round trip will have a speed of light delay of 12 hops * 10 000km each / 300 000 km/s speed of light. That's 400ms from finite speed of light. Switches, routers and relays along the way will add to that."
"both the client and the hidden service establish a three hop circuit to the same tor relay, where the connections are joint, so hidden services will have even double the delay of normal tor traffic. If relays were homogeneous distributed among the globe, two random relays will be 1/4 earth circumference apart on average. This means that a round trip will have a speed of light delay of 12 hops * 10 000km each / 300 000 km/s speed of light. That's 400ms from finite speed of light. Switches, routers and relays along the way will add to that."