But frame-by-frame cel animation - which involves weeks, months, years of tedious drawing - has been comprehensively disrupted by upstarts like Anime Studio (http://my.smithmicro.com/anime-studio-pro.html), which uses bones and inverse kinematics to produce quality animations quickly and easily.
Then there was Creature House's legendary LivingCels - the animation version of Expression (https://en.wikipedia.org/wiki/Creature_House_Expression). Imagine something as capable as Adobe Illustrator, but with a more intuitive interface and simpler workflow; then imagine using it to create complex animations using natural media brushes. That was a big development in 2002 (some predicted it could displace Flash), until Microsoft acquired the company, had no idea what to do next, and thus quietly killed a revolutionary product.
Aside: the original Creature House version of Expression is still available as a download from Microsoft (http://www.microsoft.com/en-gb/download/details.aspx?id=3124...). The Mac version is PPC only, but the Windows version works flawlessly in WINE on Mac and Linux.