Via Ole Eichhorn, the UK Guardian's Survival of the Unfittest:

Lotus Notes is used by millions of people, but almost all of them seem to hate it. How can a program be so bad, yet thrive?

We've all had bad software experiences. However, at one of my jobs, our corporate email client of choice was Lotus Notes. And until you've used Lotus Notes, you haven't truly experienced bad software. It is death by a thousand tiny annoyances -- the digital equivalent of being kicked in the groin upon arrival at work every day.

I won't say that Lotus Notes was the reason I quit that job, but it was definitely a factor in my decision. The UI is the application.

Lotus Notes is a trainwreck of epic (enterprise?) proportions, but it might be worth studying to learn what not to do when developing software.