Just kinda wondering…
Where’s the option zero? 
Depends on what you define as own? I have 2 for my business that I pay for and use, but then I have a bunch more that are technically my customers, but I usually will register and pay for the first year of the domain when people sign up to host with me. That will change soon though as I am setting up an autopilot system where you can register using your Credit Card and the system sets everything up for you, then you will need to register your own domain name.
Ok, I added my 2 cents, I am done.
There you go… I have added ZERO just for you!
I own around 8 domain names. I wont be renewing some of them this year and after that I will only own 6 domain names.
I have 2
a personnal one and a professional one 
I have 3 domain , currently 3 domains are running, 1 for my personal and other 2 for professional…I have taken services from hostgrant…
4
Four!
I own 3. My personal site, my free webhost, and my mums business domain which is goin down this year. I’ll most likely be registering a new one, or two in the next few months.
This just went up by 5 as i’m starting a free-forum hosting service using my own forum system.