I am an avowed Eris lover. (See my past posts for evidence.) However, I have had a couple of issues.
Got the phone Dec. 24th. About two weeks ago I started to occasionally get an "android.process.acore stopped unexpectedly pls try again later.force close" message. When it first happened it was frequent. I tried a few things (uninstalled recently installed apps, cleaned up contacts (there were some weird duplicate groups in my gmail contacts)) and got it to where it wasn't happening much. Now it happens on average of once every day or two. There are no ill effects from it, just makes me click ok.
Then last night, for the first time ever, the phone locked up. I had just hung up from a call, it ended the call then hung. Nothing worked on the touch screen, only the power button. I eventually had to pull the battery (though I later realized I could have used the touch pad).
Then this morning another lock up. After a missed call. Since the touch screen wouldn't respond I had to pull the battery (couldn't unlock the phone and won't allow a power down while locked) again.
Has worked flawlessly ever since.