Mustrum_Ridcully
Legend
The level 29 daily in the swordmage preview is a reliable attack power that, as an effect, increases your crit range to 19-20 for the duration of the encounter. (This is nice for the swordmage, who--lacking Dex--would otherwise probably not be able to get Heavy Blade Mastery.)
The problem? Since it's reliable, the swordmage has a considerable incentive to miss with the power--so he can improve his crit range for another encounter, too.
The correct response, probably, is just to not make the power reliable or limit the crit benefit to a hit--but, by RAW, how exploitable is this? Can the swordmage choose to "attack the darkness" or whatever with the power whenever he wants--retaining the crit benefit all day long (he'd just "miss" with it again every five minutes or after every short rest), until the end of the encounter where he actually uses it successfully (thereby expending it)?
Dang, I wondered about that power, too, and wanted to post on it.

But I wondered more about the implications of the power - how do "reliable" and "effect" or "miss" effect stack. The simplest answer - and I presume also the correct one - the power is not expanded on a miss, and you get the miss/effect benefit anyway.
That's in interesting way to create something like "Reserve Feats" or the 3.5 Psionic Focus. You can gain a benefit if you do not expend a power.
Interesting thing is that this is more or less an emergent feature of the rules - and until we saw an example of it, we didn't necessarily assume that was possible (or intended/allowed).