I will discuss the lowest-column density cold HI clouds, originally discovered by Braun & Kanekar (2004) and recently confirmed by Stanimirovic & Heiles (2005) using the Arecibo telescope. These cold clouds have HI column densities of ~10¹⁸ cm^-2, below an observational lower limit derived by Heiles & Throland (2005), and also below tiny-scale-atomic clouds detected by VLBI and time-variable profiles against pulsars. These column densities are close to the minimum imposed by thermal evaporation. These observations, as well as a flurry of numerical simulations, are starting to suggest that interstellar `clouds' may be more transient phenomena than what was traditionally thought.

I will also present results from a very recent application of the pulsar spectroscopy for studies of the interstellar medium, which resulted in the discovery of pulsed OH maser emission stimulated by a pulsar.