As a language acquisition researcher living from 1928-1976, much of the work Pimsleur published during his lifetime reflects the audio-lingual tradition prevalent at the time in which he lived. Communicative language instruction is viewed by many as a counter reaction that broke from the shortcomings of the previous audio-lingual methods, so it may appear strange then that I would be still be mentioning Pimsleur on an academic website well past the establishment of CLI. It is, however, not the work Pimsleur published during his lifetime that is relevant here.
Rather, as a French teacher at UCLA, Pimsleur himself was highly frustrated with the shortcomings of the audio-lingual tradition and sought to develop methodology for improving it. He wrote a draft for a manuscript outlining his theories on how language teaching needed to adapt, then died shortly after. Thus, his later work never circulated through academic conferences and publications. His wife, however, did pass his manuscript onto Heinle and Heinle corporation which, after a series of corporate acquisitions, resulted in the extensive Pimsleur Series library offered by Simon and Schuster corporation today. Naturally, the corporate entities currently capitalizing on the Pimsleur methodology have little incentive for convincing anybody but end-consumers in the value of Pimsleur's now public-domain methodology. Consequently, his final work is currently unavailable at any major online bookstores or search engines -- leaving only a few copies scattered in various libraries and forgotten in most academic work.
If we examine either Pimsleur's theories or the product line developed around them, it turns out that in many ways he advocated a greater departure from audio-lingual principles than Krashen. Whereas Krashen advocated a balance between language learning (monitoring) and language acquisition, the Pimsleur approach uses no meta-linguistic monitoring. Both sought to use child language acquisition as a model for understanding "natural" (Krashen) or "organic" (Pimsleur) approaches to learning. Both emphasized the importance of comprehensive and dynamically incremental input. Both suggest role play as an example of a key activity. Separated by only a 20 minute drive up the #10 freeway, we can imagine that both were facing a number similar problems and seeing similar trends.
The two differ in that whereas Krashen's principles and other subsequent innovations in language pedagogy have had a major impact on reshaping the foreign language classroom, Pimsleur's principles, have dominated the market for outside-of-class learning. We could simply leave it at that, presuming that the two theories are successfully addressing the areas best suited to them. It is important to remember, however, that homework assignments often make up a significant percentage of students engagement with foreign language materials. Unfortunately, innovation in foreign language homework curriculum often lags far behind materials design for in-class usage.
Given that the Pimsleur approach has already proven wildly popular with out-of-class learners, we could reason that it could also be applied to strengthening homework materials. For students, the proliferation of iPods and similar technologies has removed the clunkiness once associated with auditory homework or the need for sitting in dedicated "language labs." On the production side, the rising popularity of amateur podcasting has resulted in extremely powerful, free, software solutions, unprecedentedly cheap condenser microphones that don't even require pre-amps and other advances in sound recording that go a long way in addressing cost concerns.