I've spent about a dozen days on both the QST-106 and 99. Compared to its predecessor - the Q-105, the 106 with the added carbon layer and metal underfoot is definitely smoother, more damp and stable, and has more power out of the turn. But without full length metal, it does still retain a light playfull feel. I think with these modifications, Salomon is searching for the sweet spot with the QST line. They may have come close to nailing it.
Between the QST-99 and 106, I feel well covered for a west big-mountain resort. The 99 for groomers and bumps, and the 106 for bowls, high alpine, and powder. Either one are great in the trees depending on snow depth.
Speaking of snow depth, we recently had a big 15" day at Breck and I brought out my Q-115s from last year and went for first chair. After several runs, I switched to the new QST-106s and actually liked them better in everything up to knee deep. Comparatively, the flotation was still great and maneuverability superior.