Not having a diploma is all I know. As an autodidact myself I have come across situations where people simple stop job-negotiations if you don't have the papers. I could consider it a problem but on the other hand I am thankful I will not end up in companies where status matters that much. Other than the job opportunities there are a few things which might be a little tougher:
- learning what you don't know compared to when you're being offered something new. Especially if you want to learn something valuable in the business while you don't know the business yet. In this case a curriculum is beneficial.
- You might not get into the naming of stuff. There are plenty of things out there, especially principles that are referenced which are harder to grasp/remember when you haven't seen them as much as an ordinary student has. This limitation can be overcome by repetition and keeping up your knowledge. Something everyone needs to. But still, it might take more time and effort.
- A different way of thinking. I think a lot more autodidacts are focused on finding a solution whereas a proper education will force you into analytical thinking. On the other hand, anyone who has enough passion for IT to learn developing code must in some sense have analytical thinking capabilities otherwise you wouldn't do/want to be in IT. But for some people it will make a difference.
Looking at What are your best career advice for student developers? i see mostly non tech arguments. Many of which aren't in the curriculum. The are more or less personality traits. I think those are more important then the education you receive.
Great question, like @martinczerwi I am eager to read what others have to say.