Summary: Let advanced users hack on your products. They will come up with innovations that you didn't think of.
This stands up nicely to an economic interpretation too: If someone is willing to take the time to hack around and build something that wasn't part of the spec, that means that they're willing to spend capital to have that functionality. Which means it's some sort of market opportunity.
Enterprise software can often be maddening like this: companies sell their software for $200k + and they want to be gatekeepers and prevent customers from getting into the code -- they want to preserve the mystique or something. But often they just end up being roadblocks to customer happiness. Like, I bet if we could have hacked on Oracle Calendar rather than having to build our own totally separate version, we'd be vastly more advanced than either system ends up being. Good, complex software takes time (a lot of time) and figuring out how to build on the accumulated knowledge of others (represented in code)
Unfortunately, the article puts this technique in opposition to "traditional" anthropological design processes -- which often aren't well-integrated anyway. There's absolutely no reason why you can't derive benefit from both techniques.
(...I was thinking about calling this post "Ellen on Joel on Software" but I think that would be a gross thing to say.)
We had a thread on the UE team mailing list where someone had -- reasonably -- gotten a bit miffed that Joel Spolsky blithely assumes that most of usability and design are trivial functions that anyone can easily do anytime. One of the Joelisms she cited from User Interface Design for Programmers was:
if usability engineers designed a nightclub, it would be clean, quiet, brightly lit, with lots of places to sit down, plenty of bartenders, menus written in 18-point sans serif, and easy-to-find bathrooms - and nobody would be there? (p. 130)
I am generally a huge fan of Joel on Software -- although I am a bit annoyed by his attitude towards my profession -- and to lighten the mood, said this as part of my message in the thread:
...and by the way, we all know that usability engineers would never design a brightly lit nightclub. you'd do some contextual interviews, learn that no one really wants to see each other in a nightclub because the primary user motivations are getting laid and drinking away depression, and obviously the place would need to be dark. at which point the designer would come along and suggest putting the menus with 18-point type behind lucite slabs (protects against spilled drinks, too!) with LEDs embedded in the top edge. ;)