Starting with Windows 7, the application manifest is becoming more and more important.
In Windows Vista, you need a manifest to bypass the application virtualization. In Window 7, you need a specific application compatibility-manifest to get correct API function behaviour 😉
For example, a race condition in GetOverlappedResult is only solved, if you explicit specify in your manifest, that you want a correct behaviour of this function.
Also a bug in CreateFileEx is only solved if you specify this in your manifest.
Of course, this is in general not a bad idea. But the manifest only allows to enable all new features or nothing. There is no way to exlicit enable only one of the bugfixes.
Here is just a small document of the “Windows 7 – Application Manifests – Compatibility”.