According to Ghostcrawler, between patch 3.0.3 and 3.0.8 elemental shamans should see 'a total of about 20%' more DPS, depending on gear. Since they announced their 3.0.4 talent changes for the spec, they've made more changes which are currently live on the PTR for 3.0.8, and they estimate that each round of changes should increase DPS by about 10-12%, combining for the 20% estimate.
Since these changes haven't gone live yet, your guess is as good as mine as to whether or not they'll all combine to meet or even exceed GC's predictions. My shaman's elemental gear is solidly in that category of gear he states 'won't see quite such a lift' so as soon as I manage to get on the PTR and test it, I still won't be in the gear needed to really verify this.
Now all we need is to either fix mail itemization for elemental or let our friendly caster shaman get leather items drama free, and elemental will be in a good place.