EDIT: here's how to change your primary google account and keep everything happy without wiping your phone!
Credit to someone else... not me!
If you want to change your primary gmail account for Gmail, its much easier.
Don not hard reset means set to factory defaults , by erasing all data and application , instead go to
1. Settings -> Applications ->Manage Applications ->
Here you have to "Clear Data" from
1. Gmail
2. Gmail Storage
3. Gppgle Apps
4. Google talk and Talk services
5. and IM. (Would be rare to have this showing unless you are using Google IM)
clearing data is much simple just click on aplication and clear data.
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the Dev also warns that Google Storage will want to keep filling up so do that one last before exiting Manage Applications section.
Then, of course, you must regularly restart your phone, when it comes back, you will need to enter your new chose gmail, then follow the instructions. You also should do a *228, 2 for OTA, but may not be needed. What may be needed is having to do a *228 , 9 (as previously instrcted at any Verizon Store when you bought the phone in the first place).
This method of changing the an Android devices primary gmail account actually works. So let's all stop the goddamn FUD that we can't change the primary email AND LET CUSTOMERS KNOW and/or right a batch file with a shortcut in Manage Applications so that we can just stop all this bickering. Now this next part is probably why Google, Android Market, Verizon employees, Motorola CS employees are all saying "it can't be done", is probably due to the next relatively complex procedure:
The apps PURCHASED need only be re-registered, but in order to NOT Download and pay for them again, you will have to remove your CC from the old gmail/Google Checkout and use it in Google Checkout with the NEW gmail you have chosen for your new Droid primary - sure beats re-DLing and installing all those apps. Unfortunately the CC has to be the SAME CC you used on the old gmail account otherwise you ARE stuck with re-purchasing the apps from the Market using the NEW gmail you have chosen along with the different CC/Google Checkout.