The "Inform 7 Programmer's Manual" by Ron Newcomb explains Inform 7 from the point-of-view of someone who knows how to program in other languages. Version as of August 15, 2011: http://www.plover.net/~pscion/Inform%207%20for%20Programmers...
An older 2009 version (if PDF is a problem): http://www.plover.net/~pscion/inform7.html