This is why I believe the 650 SUCKS. Let me preface this by saying that I love Logitech products (not just the remotes), but my bitterness towards their Harmony products is at an all-time high.
So... I loved my 670, but it conked out due to an abnormal amount of punishment (kids). Called Logitech, and they were good enough to give me 50% off any remote on their website. I chose the 650, and I LOVED it. What an upgrade!!! Shortly after though a problem developed. I noticed that after I chose an activity (like Watch TV), I'd set it down in my cupholder (home theater seats). When I went to go pick it up again and looked at the screen, it was no longer on the "Watch TV" screen but on the "Choose an Activity" screen. At first I thought maybe my kid pressed a button, or maybe I did and didn't notice, but it started happening more frequently.
Long story short, I found that any shock to the bottom of the remote (like when you put it in a cupholder) will oftentimes reset the remote to the Choose Activity screen. Now by "bottom", I am referring to the opposite end of the remote from where you plug in the USB cable. In case you are wondering, I babied this remote... I wasn't slamming it down into my cupholder or onto the floor. At first, I thought maybe the batteries were losing contact due to the shock, therefore reseting it. I tried creating a tighter fit by bending out the contacts a bit... a no go. Tried using folded up pieces of aluminum foil, no luck. Since then, Logitech has tried to replace the 650 two times (been through a total of 3)... all of them had the same problem, even out of the box!
So last week, I called and asked them for another replacement, but this time NOT a 650. They acknowledged that the reset problem was a known issue and that they would send me a 700 at no extra charge. They claim that even though the 700 is nearly identical to the 650 (just comes with rechargeable AA's and can control one more device), it does NOT have the reset issue.
Just got the 700 today, and I will say that out of the box, it looks like Logitech was right. I tried tapping it on the bottom (hehe) and no reset. I'll see what happens after some regular use and provide an update.
I encourage you 650 owners to test it out yourself. Choose an activity first. Now, tap the bottom of your 650 remote with the back of your hand with light-moderate amount of force (realistic to what it would face in the real world). If it doesn't reset, then lucky you... and unlucky me for getting 3 defective ones in a row.