On the phablet debate, I've been carrying both a smartphone (Moto Photon Wimax - it was the first 4G/global capable available which is why I got it) and a Nexus 7 3g since the 7 came out. My use is much more tablet than phone so I have been interested in combining the two into one device.

After the Note 3 announcement I concluded that a 5.7" screen wasn't going to do it for me. So I decided to go with a Samsung Mega on AT&T. I tried to see if I could get one of their phones and get it unlocked relatively soon as I travel internationally and I prefer local SIMs when I do. Unfortunately, after talking to a bunch of people at AT&T, it became clear that the phone might never be unlocked as it is a phone specifically for AT&T.

I bought an international one (HSDPA with Euro/Asia LTE), got it two days ago and put a prepaid plan with AT&T in it. Observations:

1. It is quick and responsive for what I do (am not a gamer) - basically email, Web browser, music/movies, travel, etc
2. Screen feels effectively equivalent to Nexus 7 but device is much smaller due to relative size of bezels. N7 could be made much smaller with a smaller bezel.
3. Screen is big enough that it has a tablet feel - doesn't feel cramped.
4. I have it in the minisuit case and it fits easily in pant pocket and jacket breast pocket - latter was a problem with N7 on some jackets.
5. If you're going from a phone to this, it would feel huge but if you're going from a tablet & phone to this, you'll feel like it's small and you've both lightened your load and simplified your setup.
6. Minimal data at this point but you can imagine I have been beating on it and the battery has held up well. I have a spare/outboard charger coming but I think one an get through a day with one battery. I think the case helps as closing the lid causes it to conserve power.

If your use case fits, it is a good choice. I considered the Sony Xperia Z Ultra but it's not out yet and it doesn't have a replaceable battery so it didn't make the cut.