Katie -
Most Product Managers, will have an engineering slant, if not a full blow engineering background – which is essential. As already stated they create products, determine the what, when (market timing for releasing whole products, major and minor features) and also the how (do we deploy first on Windows then Linux or visa versa, Java or C++ for the core server, this widget requires an admin gui, and this widget needs a CLI, use an OEM component or build your own, these two components need a minimum performance spec of 100 transactions per second, they must be multi-threaded and abstracted from the OS and server so they can run anywhere, THESE ARE THE HOW, etc. etc. etc.). And the Product Marketing function provides the outbound marketing for the product. The problem when a company gets these two functions confused and Product Marketing tries to create product is that there is a huge divide between the typical Product Marketing function and Engineering function, so a huge amount of details (the how) gets lost and the end product becomes a toss-up in terms of meeting industry requirements - for being able to be deployed within a target technical environment, maintained by technology administrators, upgraded and patched, etc.
Well established products (a toner cartridge) needs Product Marketing; industries requiring early adopters, or invigoration and new direction and innovation need Product Managers.
Good Luck,
Peter
September 2008