How do you file a bug report for Windows?
Where can I suggest improvements for MS Windows 8? I've been searching for a link where I can suggest improvements for Windows8 probably for a half an hour!
For specific apps, there is usually a "submit feedback" option under settings, accessible from the charms bar, where you can send a note to the developer. Microsoft apps have this as well (I submitted suggestions and bug reports for the People app, for instance).
If you encounter any error messages, usually they will be flagged and allow you to send the information to Microsoft about what triggered the error. Microsoft triages this information, culled from thousands or even millions of installations, to help them debug the operating system or gather usability information. Occasionally you might see them logged in the Notification Center, and it can let you send the information to Microsoft if it hasn't already. Do so, and it will help Microsoft debug the issues.
Also, as you use the software, they will typically allow you to participate in the Customer Experience Program. What this does is log usage information about how you are using the software, which they can use to determine how people interact with it and what people do and don't do. They use this information when designing elements of the operating system and associated software to improve the interface layout and information presentation, as well as determining what features to add and what aren't used and can be removed.
Also, you can make some noise on Microsoft's support page. They maintain a site called Microsoft Answers. While it often can be a headache to use (I personally think its moderation team is no more helpful than telephone operators reading from a script), and the actual dev teams don't participate directly on there, but if there is enough noise surrounding a particular bug or feature implementation, they can take notice.
And aside from that, it can also help to have inside contacts. This is only something that will develop through personal networking, and I'm not going to volunteer anyone on their behalf, but sometimes they might be in a position to put some internal pressure on the Windows team to consider certain changes.
I don't believe there are other options available for us users, unfortunately. However, these are options that can be of use.