Merging buildings? Re-assign offices from scratch

When Lockheed and Martin Marietta merged their headquarters into a building previously occupied by Martin Marietta, they moved everyone out and reassigned offices from scratch. This avoided the impression that anyone had been bumped or that some people were more important than others. That action was critical from a social standpoint. "The attitude 'we bought you' is a corporate cancer." (Source: HBR article, 1997)

Same thing with P&G:
Following the P&G acquisition of Gillette the day came for Gillette staff's site merger into P&G's offices.Tarek Farahat, P&G's country general manager, arranged that when people arrived at the facility on Monday morning nearly everyone from both companies were in new offices on new floors.

Biggest Mistakes in Business

Apple co-founded Steve Wozniak was an engineer at HP, and he gave it the first shot at his microcomputer idea. They said no. Source: Dan & Chip Heath in Fast Company

Dyson approached all the major vacuum cleaner manufacturers to license his technology, but they turned him down. Hoover were later found guilty of patent infringement. Source: Wikipedia entry

(add: 3M turning down WL Gore products)

Brand extensions across categories - good and bad

DISNEY
Good: Disney 'Fairy Tale Weddings' bridal wear. Disney branding kept subtle and tasteful.
Bad: Walt Disney Signatures $1,295 executive fountain pen.

HARLEY DAVIDSON
Good: footwear
Bad: Xtreme cake decoration kit

IAMS
Good: pet insurance