I have been wanting to get CP8 running for the new features. I had 7 preinstalled on my factory ROM, and have since upgraded to wm6.5 with v7 installed, but it wont let me upgrade to 8 via the website. Now it's only £2 more to buy it anyway so I thought I'd do that but with all the problems on this thread I decided to contact support to try and get a definitive answer. After several weeks here is the response:
"We are compatble on the HTC Touch Pro 2 and HTC Touch Diamond 2 if you do not have CoPilot 7 installed. There is a bug in the HTC ROM that HTC are aware of on these devices which means that once CoPilot is installed, we cannot uninstall CoPilot in any way. For new customers that do not have a previous version of CoPilot installed, we are 100% compatible. For existing customers we are working with HTC to find a workaround to this problem but currently cannot provide a timescale on when this will be resolved. There is a workaround if you are willing to carry this out, and that is to manually delete the 2577 and CoPilot folders on your SD card and please make sure you delete also delete the "cpl7" and all other files beginning with "copilot..." in the Windows folder on your device.
Afterwards, you would need to perform a complete hard reset of your device.
Some customers did managed to delete all of the CoPilot 7 files by upgrading the ROM version from 6.1 to 6.5.
This currently is the only way to get CoPilot 8 installed onto the device cleanly at present. Sorry for the inconvenience."
Might just stick with 7 to be safe!