Peeling of a viscoelastic adhesive from a solid substrate poses a wonderful problem of polymer flow. When the adhesive is peeled, it is also stretched in a direction normal to the substrate. The concomitant Poisson contraction creates a pressure gradient and thus induces a shear flow in the adhesive close to the delamination front. Earlier it was pointed out that the strength of viscoelastic adhesion would decrease if the shear stress in the adhesive is relaxed by a slip process at the interface. Here we report experimental results which confirm that viscoelastic adhesives do indeed slip on segmentally mobile organic surfaces at and near the crack tip regions. Evidence of slip was obtained from the interfacial displacements of small fluorescent particles when the adhesive was peeled from various substrates. While on most surfaces the slip distances were about 1-2 mu m, a large slip (13 mu m) was observed on segmentally mobile tethered chains of polydimethylsiloxanes (silicones). On the latter surface, slippage is so extensive that the adhesive flow pattern near the delamination zone is like plug flow. We believe it is due to the propensity of huge slippage that the silicone-containing polymers exhibit their unusually low adhesion to most materials.