The Sensor Cube platform is an ultra-compact, modular and power-aware way of building sensor networks; they are based on a stackable hardware design supported by a Tiny OS based operating environment. The Sensor Cube hardware measures 14 × 14 ×18mm³ and features an integrated coplanar antenna, a design that results in an ultra compact footprint. A core characteristic of the system is that its modular design allows for each of the radio, processor, sensing and power management layers to be interchangeable in a Lego-like manner. Moreover, its low power radio (based on the 2.4GHz Nordic nRF2401 design) and microcontroller (based on the Texas Instruments MSP430) allow for very efficient operation. The Sensor Cube operating and software development environment is derived from Tiny OS, which has been modified to meet the hardware requirements, in particular by introducing a power-aware and reliable ALOHA-type MAC protocol. In this paper we present our experience with the Sensor Cube platform and, in particular, the implications of its ultra-compact design on system performance, specifically as it relates to the characteristics and limitations of the radio unit.