Used it back in 2006 for company email, policy documents and software issue tracking - both enhancements, bugs etc. raised by product management, development and client facing services.
It was a mess. A slow, grinding mess of unusable screens and panels. If you end up typing things in an external text editor simply to copy-and-paste it in just to guarantee you don't lose your work, you know something has gone terribly wrong.
Got a friend whose company were recently bought by IBM and they "eat their own dog food". He's not happy to be now using Lotus Notes.