I'm on a bit of a warpath at the moment with PE. So here are some myths about it, and their busts.
Myth: it holds you back
It also doesn't mean spending all your time getting things to work on older browsers. You're starting with something simple enough that you know it will work there so that you can spend more time with the fun, fancy, stuff for more capable browsers.
PE is actually about dealing with unknowns: we don't know the user's browser, what their network connection is like, or if they have any disabilities. Building with PE means not caring if a user is running IE6 on Windows XP or Android 5.0.1 on a Sony Xperia Z3: you know that your site will still work on those, and on whatever is released next week and next year.
Myth: it only works for small projects
A modern front-end web workflow is all about making modular, re-usable, components. Even very large web things (apps, sites, wotsits) are essentially made up of a lot of repeating patterns. Building these modules up with PE in mind means building your large, complex, project in way that will work for everyone (albeit in different ways).
This was actually a bit of a run up to what I really wanted to write about: Getting better at Progressive Enhancement.