1. it does not work on top of other multi-touch applications (e.g. mspaint and the apps in the microsoft touch-pack) as to not interfere with the touch input for these apps.
2. if you are running on 64-bit windows, the tap gesture will only work on 64-bit applications (and not 32-bit applications). So IE on 64-bit windows is a limitation, since 32-bit IE is the default browser on 64-bit windows. If you run 64-bit IE you will notice that the tap gesture works.
Do these limitations explain the behavior you are seeing, or are you seeing something different? If you can provide specifics about what app you are running where the tap gesture doesn't work, I can try to repro it here to let you know if it is expected behavior, or maybe a bug that can be fixed. Thanks for your input!