Oh, I wish I could already quote-boost this post!
MapInfo was my first contact with GIS. In 2006-2007, when I was a student in urban geography, I used it to build a GIS of gated communities in Marseille.
MapInfo was as powerful as it was a nightmare in terms of user experience. I don't miss it, but using it taught me that even the least intuitive tool could be used with minimal hassle with a rigorous #RTFM approach :)