Depends on where you live, how many dependents you have, retirement goals, etc. It is really a broad question.
There are the digital nomads who are happy to move around the world, live out of a backpack, etc. My feeling is that they don't need very much to live that lifestyle. However, it strikes me as a lifestyle that appeals to bachelors who are in their 30's or younger. So what I'm saying is that while basic IM is a great way to fund your travels, the scene changes once you get married and have kids...now you need a house and car, and saving for your child's education and retirement requires serious cash.
For some, a 'good income' is any amount that is equal to or greater than what they could earn in a so-called 'real job'. This means it would be answered differently if you're a bin man or a GP.
You can also live on a whole lot less in some countries than others, so again, it depends.
For someone living in a major world city, I'd think you'd probably want to shoot for $100k/yr.