Many modern and future technological applications involve ultrathin polymer films with a thickness below the 100-nanometer scale, where statistical bulk averaging is jeopardized and interfacial constraints dictate transport properties. In such confined polymeric systems, transport properties strongly depend on molecular relaxation and structural phases that deviate from the bulk. One of the processes that is thereby of foremost importance is the glass transition. In this paper, we investigate the glass transition value as function of dimensional constraints in ultrathin spin coated polymer films (e.g., polystyrene). Its non-monotonic film thickness profile is tailored with appropriate molecular weight and crosslinking density, and utilized to optimize the performance of a nano-electromechanical system (NEMS).[1] The length scale of dimensional confinement over which the glass transition value differentiate from its bulk value is compared to the direct spatial observation of the cooperation lengths on cooling towards the glass transition. Besides a highly accurate method to determine the glass transition of ultrathin films (shear modulation force microscopy (SM-FM),[2] an elaborate scanning force microscopy (SFM) friction-velocity temperature analysis is introduced as a material characterization tool.[3] It provides a model-independent spatial analysis of the molecular cooperativity during the glass forming process of polystyrene. Our intermolecular friction analysis yields a cooperation length that increases from the monomer scale (0.3 nm) to 2.1 nm clusters, when cooling from 30 K above Tg. Deviations from the power law behavior closer to Tg, suggest that long-range processes, e.g. the normal mode or ultra-slow Fischer modes, may couple with the α-relaxation, leading to energy dissipation in domains of tens of nanometers - a length scale that is important for films of comparable thickness or material multiphase systems with critical dimensions on this order (e.g., nanocomposites and blends). [1] S. Sills, J. Frommer, Wilson Chau, Victor Lee, Bob Miller, Craig Hawker, R.M. Overney, Interfacial Glass Transition Profiles in Ultrathin Spin Cast Homopolymer and Crosslinked Polystyrene Films, J. Chem. Phys., 120 , 5334-8 (2004). [2] S.Ge, Y. Pu. W. Zhang, M. Rafailovich, J. Sokolov, C. Buenviaje, R. Buckmaster, R.M. Overney, Shear Modulation Force Microscopy Study of Near Surface Glass Transition Temperatures, Phys. Rev. Lett., 85, 2340-2343 (2000). [3] S.E. Sills, T. Gray, R.M. Overney, Molecular dissipation phenomena of nanoscopic friction in the heterogeneous relaxation regime of a glass former, Chem. Phys. Lett. 123, 134902, (2005).