It turns out that some Nexus One owners running CyanogenMod 6 (CM6) have been experiencing issues when trying to update a handful of system apps. As such, XDA-Devs forum member unforgiven512 has thrown the updates into a tidy package. The updated apps are:
Amazon MP3 Google Maps Google Search Google Voice ROM Manager Street View Superuser TalkBack Voice Search
Not only does this fix the app updating bug, but it moves the app info from the "data" partition to the "system" partition. There are two benefits to doing so:
2. Updates to system apps are stored on the "data" partition. This uses up your available space. By flashing this update, the updated files will be stored on your "system" partition -- where they belong, instead of your "data" partitions, where the files get placed when you update from the Market.
3. I'm not 100% sure, but I have a good feeling this is the final fix to problem #1. I believe this causes Android to update the signature associated with the app, "correcting" itself.
Better still, installation looks to be as simple as flashing the update.zip through recovery. That said, it also looks like a minor few people who have tried to flash the update have received no signature errors.
If you're having issues updating these apps on your CM6'ed N1, download the update and give it a go, and be sure to let us know how it goes.