If you own an ASUS P527, you can upgrade it to Windows Mobile 6.1 courtesy of the latest firmware from ASUS. It certainly took a while, considering that we found out about the upgrade back when Windows Mobile 6.1 was announced last April.
The new firmware includes the Windows Mobile 6.1 upgrade as well as some additional updates. These include enhanced decoding efficiency of multimedia playback, an updated modem firmware and more.
Different versions are available for different markets, including North America, Singapore, Hong Kong, India, and more. For some reason, the upgrade is not available for some countries though. If your market is not listed, you may need to bug ASUS in your country.
Note: The update will replace the current ROM image and will erase partnership and all user data and programs on your device. Be sure to back everything up before you start.