If you have a developer version of the T-Mobile G1 Google Android phone you might find the new Android 1.5 pretty interesting. The Android Development blog makes it very clear that this new version is for developers and not for those who use Android devices for daily, normal use.
Installing is not hard, as HTC has clear directions and the image packages needed to updates your developer Android device.
Those who do not have a Google Android developer phone will get the update sometime in May. If you have a normal T-Mobile G1, you may not want to try to update using the HTC images and methodology. Just relax and wait for the update.