Tim O'Reilly on Various Library Standards & Applications

(Okay, so he's not directly addressing things like Z39.50, OpenURL or ILS's, but you'd think the same rules apply.)

Under the heading "Lightweight Programming Models", he lists the following "significant lessons" (in abbreviated form):

1. Support lightweight programming models that allow for loosely coupled systems. [...]
2. Think syndication, not coordination. [...]
3. Design for "hackability" and remixability. [...]

Go ahead and read the whole thing...