First of all, this does not affect iTunes customer accounts—this is a different system and all iTunes customer information is completely safe, Apple told me.
If you’re not a developer, rest assured, your information is safe. For the rest of us however, there could be some leaked info, but nothing critical: mostly names and email addresses. Credit card info is secure, and app-related info is also safe.
The most damaging issue for most of the affected developers is having to wait for the portal to be back up. This is a particularly busy period for developers, with the next major versions of both OS X and iOS in an advanced beta stage. Let’s hope Apple can fix this soon.