Konami did give me one demonstration of how the touch screen comes into play and it's quite impressive. In past Castlevanias we'd come upon a very high ledge that we could only reach after attaining some secret ability, and while you'll still gain new powers you can get to seemingly unreachable areas with a few finger taps. Right from the get go I encountered a bridge that had these blue crystals hovering above it, and using the stylus I was able to actually carve a ledge that Soma could use to get to a new area.
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Hrm... sounds kinda funky to me. I'm still not sold on the whole DS idea though, so I may be a bit biased here. Too bad we can't get a PS2 sequel to SotN...