Randall's ESL Cyber Listening Lab is one of the better sites I have come across for listening practice for ESL/EFL learners. The wide variety of skill levels and cultural topics provide fertile ground for any number of learning assignments, whether instructor-led in the classroom or as autonomous student practice.
The single (and minor) negative point of using this site--as one commenter has already mentioned--is the somewhat distracting nature of the Google ads on each page. In particular, these interrupt the physical "flow" of individual activity pages; for example, there are ads that separate pre-listening and listening exercises, which may confuse lower level learners or even more advanced learners not overly familiar with the physical layout of web pages.
While I have not yet used the "Long Conversations with RealVideo," there could conceivably be a problem with in-class use of these with numerous students attempting simultaneous downloads in a language lab with lower connection speeds.
Time spent reviewing site:
4-5 hours over the course of several classroom sessions.