When you have a power contingent on an enemy moving...

[Nail]

Page 285. But to me it doesn't appear to be referencing cases like this, just noting the fact that forced movement doesn't use up your movement:

Agreed.

I see the text says "Not a move", meaning it's not a move action. The text doesn't say "Not movement".

 

[Hypersmurf]

So the question simply becomes, is forced movement....movement? Booming Blade requires movement, it doesn't say that the target has to move on his own, but simply that he moves.

As eamon pointed out earlier, the Immobilized condition states that "you... can be forced to move by a pull, push or slide".

If someone is Immobilized and is affected by a slide, what is it he is forced to do? To move.

-Hyp.