It does seem that if a smaller exchange is above the Mt. Gox rate, and the Mt. Gox rate itself is dropping, it's very likely that exchange's rate will move down as well. Similarly, if a smaller exchange is below the Mt. Gox rate, and the Mt. Gox rate is increasing, it's very likely that exchange's rate will move up.
Especially with arbitrage bots starting to show up. It'll be very fast.
Actually when you think about it, this is a mechanism that might actually synchronize rates on all the exchanges (at least the ones that have good enough apis) and finally give smaller exchanges a chance to enter the market more easily.
Just a thought...