I see the business arguments, but all of the answers are physically too big for me. I realise I am a 1% corner case but I have to be able to use the phone single handed while walking the dog and without dropping it in the mud. This rules out any kind of phablet, even the Note 3.
What I want in a phone is one handed usability, perfect car integration and efficient backup and restore, as well as the ability to plug into a monitor or projector.
The weird nature of UK contracts means that a phablet is better than a tablet (because some phone companies disable internet if you plug your SIM into a 3g tablet, but not a tablet with phone - I'm sneering at you, 3) - which means that as a second device the upcoming Huawei mediapad looks like a good option.
I can't see the argument against two devices for different use cases, but then I'm a great believer in redundancy and have an office full of kit.
The bottom line is that I still have a BlackBerry as a phone but I have an Android tablet that will be replaced with a phablet at some point, with a PAYG account for those times when it's out of reach of an 802.11 network. If BB had died I might even have a Windows phone. I just don't like to rely on one OS for mission critical communications.