The dynamism and heterogeneity in ubicomp environments on both short and long time scales implies that middleware platforms for these environments need to be designed ground up for portability, extensibility and robustness. In this paper, we describe how we met these requirements in iROS, a middleware platform for a class of ubicomp environments, through the use of three guiding principles — economy of mechanism, client simplicity and levels of indirection. Apart from theoretical arguments and experimental results, experience through several deployments with a variety of apps, in most cases not done by the original designers of the system, provides some validation in practice that the design decisions have in fact resulted in the intended portability, extensibility and robustness. A retrospective examination of the system leads us to the following lesson: A logically-centralized design and physically-centralized implementation enables the best behavior in terms of extensibility and portability along with ease of administration, and sufficient behavior in terms of scalability and robustness.