[Update: see the non-lethal solution here before going for a factory reset]
If you, like me, have a Google Apps hosted website and use multiple email IDs apart from your Gmail one, you could run into a big problem with Android devices if you try to sync them all with the Gmail application.
If multiple accounts have the same contact, when Android tries to sync them, they will generate a conflict. This will crash the contact management process and show up as a [android.process.acore] error. This would create a situation where you will start to get the [android.process.acore] crash notification as soon as you start your device, forcing you to keep pressing the OK button to close the prompt, during which time everything else will freeze. The prompt will reappear frequently, sometimes as much as every few seconds, and make using the device nearly impossible.
You can stop the prompt from appearing again if you’re offline by disabling Auto-sync from Settings > Accounts & Sync, and continue playing Angry Birds. However, if you want to check your email, you’ll need to re-enable it, again causing process.android.acore to crash. Reading emails already in your device inbox is also impossible, and IIRC, even with Auto-sync disabled.
This issue affects not only reading emails in the Gmail app, but also Mail’d / K-9 and the hidden Email app (which syncs with your Exchange account and calendar). Clicking on a mail item simply brings up the acore crash prompt again, and the mail client exits.
As of now, the only known remedy is to do a factory data reset through Settings > Privacy Settings. If you have a good backup program, it would help to back your data up as well as the installed apps. The Android Market is unable to recall which applications you had installed after the reset. Mercifully, the reset does not remove your data files such as pics, documents etc., but it pays to be cautious. If you don’t back up your applications, you’ll need to reinstall them one after the other from the market, thus losing your Angry Birds high scores.
You can safely avoid all these issues by restricting the registration to only one account with Gmail Sync, and keeping the rest for alternate email programs like Mail’d. The only significant downside of this arrangement is that you don’t get the ability to group messages by conversation thread as efficiently as in Gmail (and I guess not at all in Mail’d).
I have learnt all of this at my own peril, and twice over.
All the best.