This paper provides a detailed analysis of the effects threshold voltage variations play on the reliability of bulk MOSFET transistors. It also investigates the consequences of transistor sizing on the reliability of both devices and CMOS gates. These are followed by very accurate device-level (CMOS technology specific) analyses of NOR-2 von Neumann multiplexing with respect to threshold voltage variations, taking into account both the gates' schematic as well as the input vectors. The simulation results reported here show clearly that improving the reliability at the device-level does not necessarily lead to reliability improvement at the gate- and system-level. They also reveal that the effectiveness of von Neumann multiplexing schemes depend to a great extend not only on devices, but also on the gate types (i.e., gates' topologies).