To clear up any misunderstandings, there are two different types of LED backlights, edge and local dimming.
The new ultra slim Samsungs (UE models) use edge LEDs, these are not local dimming, but they allow for the incredibly slim depths and supposedly better energy consumption. From what I've seen of these sets (admittedly in bright environments) they appear equivalent to standard cathode LCD backlights as far as picture quality is concerned, but I'm sure Phil will be able to give more objective views on this when the review isup.
Local Dimming LED, found on the series 7 and 9 last year and 9 this year, is where areas of the picture are lit at different amounts to maximise contrast ratio. Such sets are a similar depth to standard cathode lamp LCDs, but can offer potentially better picture, with a few drawbacks (usually worse input lag, "blooming" around white objects against black backgrounds).