(I've always suspected that Gmail was inspired by the old Notes mail interface, which had no 'inbox' and was based on conversation views and tagging.)
Once Notes turned into IT-managed 'groupware' and became a bad parody of MS Outlook, it became completely intolerable. End-users could no longer create databases (or even edit their inbox columns) as most systems were completely locked-down. My last two encounters with it, they didn't even use the DB/workflow side of it, it was only for mail.
http://en.wikipedia.org/wiki/HyperCard
But that was like 6 or 7 years ago. Wouldn't want to develop in Lotus Notes anymore, but I don't have any bad memories of the software.
Never really used the email functions though.
* It comes with a program "Zap Notes" which is supposed to kill it when it hangs (Wat?). A bit funny since "Zap Notes" doesn't even work for me, and I have to use a combination of greps and kills.
* The UI rendering is slow and visible. These guys haven't heard of double buffering. You see little GUI components being rendered slowly. This is extremely annoying and sluggish.
* Every little UI operation you do in this program can take seconds on relatively modern hardware. During these seconds, the UI is of course completely blocked.
* When someone at your corporate IT wants to move a Notes mail server or such -- they actually have to coordinate a reconfiguration of all the users' mail server addresses! You have to go dig in a huge, badly designed preferences dialog to make this change. This is nuts.
The list goes on and on, but I can't fathom anyone liking this software.
My first experience with Lotus Notes was in 2005 and I found it to be a bloated piece of crap with archaic email rendering, barely functioning search, and long wait times for even basic operations. I was hoping to see news that IBM was sunsetting the entire product along with the Domino servers it runs on.