After getting rooted four days ago, the T-Mobile G2 and its European counterpart, the Desire Z, finally joined the ranks of fully unlocked Android phones, which give us the freedom to replace the ROMs on these devices with something better and more custom.
It took the CyanogenMod team a few days, but the very first CM 6.1 ROM is now available for download. It will work on both the Desire Z and the G2 due to the similarities between the 2 phones. Keep in mind, this is the first nightly build and not a final version in any way - it's not even a release candidate; therefore, bugs should be expected. However, if you like to live on the edge, go ahead, flash this release, and let us know how it performs.
Note: You need to compile the Google apps (gapps) package yourself, as the CM team hasn't done this yet. Instructions, along with the gapps download link that @ciwrl gave, are below, so it shouldn't be too hard.
Yes, this will work on the G2 AND Desire Z
The CM team does not maintain the Gapps packages. YOU WILL NEED TO MAKE YOUR OWN (until an updated new one appears). And this is how:
1) Download gapps-hdpi-20101025-signed.zip (mirror)
2) Extract the zip
3) Navigate to META-INF\com\google\android in this extracted gapps folder, and delete update-binary (NOT UPDATE-SCRIPT)
4) Extract cm_vision_full-##.zip
5) Navigate to META-INF\com\google\android in the extracted Vision folder
6) COPY this update-binary to the folder in step #3
7) Rezip gapps package
8) Flash via a recovery that does not do signature checks (eg Clockwork)