I'll resurrect this rather than start a completely new one.
Curse of the Dark Dream has me perplexed, as well.
It's the Sustain Minor, it's wording is just very inconsistent with the usual power write-ups.
First off the 'whether you hit or missed' thing /seems/ to be saying the same thing as having an effect line - so, if that's the case, why doesn't it just have an effect line?
Second, the 'save ends' is nonsensical. Saves are against ongoing effects. Ongoing effects affect you at the start of your turn, and you save against them at the end of your turn. Thus, if you're hit with a save ends effect, you're generally affected by it /at least once/, barring some free saving throw out of turn. The Sustain effect of CotDD, however /isn't/ ongoing. It's a slide, which is instantaneous, on the caster's turn, not the target's. Not only does that make no sense, it also means that, as a matter of course, half the time, the power simply can't be sustatianed, because the target made it's save before the warlock has a chance to sustain it. That seems at odds with the design philosphy of 4e. The point of the new save mechanic was to avoid the frustration of 'save negates' powers that either did nothing or anihilated the foe instantly. CotDD suffers from the former, even though there's an effect that happens whether you hit or miss, it can still do nothing if the target saves.
For my own understanding, here is how I'd think the power should have been written to work the way it seems to:
Through the hit line, it stays the same, then:
Effect: The target is 'Dreaming Darkly' (save ends). 'Dreaming Darkly' is a condition that does absolutely nothing but allow you to maintain the power.
Sustain Minor: While the target is 'Dreaming Darkly' you may slide it one square when you maintain the power.
Frankly, it's a pretty wussy effect. It'd make a lot more sense for it to have an effect line that imposed an actual condition - even if a very minor one. With the sustain only working while the condition lasts. That'd at least be consistent with the general way powers are written up, and it would mean that the daily always did /something/, even if it was only to impose a condition for one turn.
Looking at other dailies, like Radiant Delirium, I don't think even Dazed would be out of line as the condition imposed.