Verizon has placed instructions for the update to 2.1 on it's website. From the looks of things it will be an over the air update and it is called "mandatory".
Link to the instructions:
http://support.vzw.com/how_to_use/droid_upgrade.html
How many will be doing this? I know I won't as I am rooted and have no plans to go back. Plus I've been running something similar to this for quite some time.
