(It's from Cityscape web enhancement
Assuming this spell doesn't just get left behind in the planet's orbit because it's anchored in space instead of the planet...
The random movement can only be on the x/y axis. Anything that requires vertical movement (except maybe stairs), is impossible to reach, be it a ladder into the basement, or a Telvanni tower that requires you cast at least levitate to reach the top floors. The random movement may allow going through walls.
That there's no way to even mitigate the random direction of movement across a huge area and duration makes this really good for killing everyone in a city (or at least its center if large enough) without destroying the infrastructure. Nobody can get to their water, food, bed or toilet without a string of natural 20s (and I'm sure there's some shenangians to make even that not apply). Since it's dismissable, you can even keep the people if your demands are met quick enough.