Gates's management style is questioned in Allen's Idea Man, reportedly upsetting employees with insults such as: "I could code that in a weekend", and the possibly more objectionable: "That's the stupidest f***ing thing I've ever heard".
The book also attests that while Allen was undergoing treatment for Hodgkin's lymphoma in 1982, his childhood friend was busy trying to rob him of his fair share of the business.
Regular readers will know of both men's love of collecting but it's unlikely they will be making any swaps in the immediate future following these revelations.
With a fortune of $10.5bn, Allen is perfectly placed to indulge his collecting passion. He is thought to own many notable artworks, including Renoir's 1877 La Liseuse, purchased for $13.2m in 2001, and Monet's 1874 work Rouen Cathedral: Afternoon Effect.
He also has a group of vintage airplanes maintained in airworthy condition, including a Curtiss P-40C Tomahawk recovered from a Second World War crash site in Russia.
Allen rounds out his collection with some fine pieces of music memorabilia, including several Jimi Hendrix guitars.
Gates meanwhile is a fan of American art. He purchased Winslow Homer's 1898 work Lost on the Grand Banks for $36m in 1998 and bought Distance Thunder by Andrew Wyeth for $7m in 1996.
Gates is the owner of Leonardo da Vinci's Codex Leicester, which he has scanned and distributed digitally, and he also loves a fast car, with a Ferrari 348 and Porsches 930 Turbo in his collection.
Both men appear high up on the Forbes rich list, further evidence of the popularity for alternative investments among high worth individuals.