All ideas that were the seeds for multi-billion dollar companies. They sounded stupid^W bound to fail at first, especially before seeing the implementation / impact: Better search engine with no sponsored listings, seamless sync and backups, short status updates blasted to your followers, better social network, animated movies that target adults, online book store (without a book store experience), $4 lattes ... Some…
Seamless Sync and Backups - This is an obviously useful concept, we just needed to wait for the technology to arrive.
Short Status Updates - Agreed.
Animated Movies that Target Adults - Animated movies originally targeted adults. Also, in Japan they have targeted adults for decades. The small group of anime fans in America gradually grew into a billion dollar empire. American companies waited for the business to be lucrative before they started making their own. How is that stupid?
Online Book Store - Might as well say the entire eCommerce industry is stupid. Selling stuff on-line is about as obvious and sensible as it gets.