At SxSW 2008, I had the pleasure of speaking on the Filching Design: When the Shoe Fits panel with Lindsey Simon (Google), and Skip Baney (Apple). We discussed the motivations, benefits, and drawbacks of reusing code or design elements (interactions, layouts, colors, etc.) found online.
An audio broadcast of the panel is now available: Filching Design: When the Shoe Fits (27.4 MB MP3)
Notes on the panel: SxSW 2008: Filching Design