I used to run in Asics Gel DS Trainers and Asics Kayano. I tried the Novablast and didn't like it - returned them. They definitely did not make me :30 / mile faster. Sarah Hall has been hyping them, but I felt unstable and uncomfortable in them.
I ended up trying and absolutely loving the Nike Pegasus Turbo 2. Sadly, they've been discontinued, but I will probably try and find a Nike replacement.