The only thing I dislike is the search to find an accountant who will use it to review my books at year-end (only 1 out of 10 accountants will use it). But that's a social problem that gets better the more people use GNU Cash and pay industry experts to work with it
I also use it for stock trading. The Python bindings let me write scripts to analyaze the performance of my past trades. I like that its all offline. I can use the GUI for entry and easily write my own code against the data. Also there is a large and helpful community on the mailing list.