None of my portfolio domains were registered. I can definetely wake up one day and start registering thousands of domains per day and ATLEAST break even because I have tried this already in small doses and has worked out for me, but I wouldn't make a fortune.
The thing is, if you register domains you can probably get a deal as cheap as $6 per reg if you register in bulk. Or maybe even less with some registrars. If you register at that cost, you'll need $0.50 per month to break even. This is a good strategy for people who have patience - which is the key in this biz btw. On your first year you may break even, but at the end of the year when renewal time comes, you can look over each domain one by one and discard all the ones that haven't made up their registration fee. Therefore, if you discover half of the bad ones, you'll probably make double the reg fee year two. That's where you profit comes in. So it is still a good trick for those that have patience. I'd also advise people to hold all their revenue from these names on the side, otherwise when renewal comes and you don't have that money saved up you will be very angry. It's a strange feeling if you don't hold onto that money and later use it from another source. You feel like you are losing money on the typos. And you definetely do not want that feeling.
Now my portfolio was built around patience. You shouldn't jump out there and start buying up typo domains. That is not the right way to do it. Right now I am building a new typo portfolio, my last one had one domain that was bought for 4k and sold @ xxx,xxx. And the funny part is that this domain was bought on DNF, with nearly 10 days into the thread starting date! So sometimes you can see optimization potential that nobody else does. That's the key. I turned the 4k domain into a mini Google adsense site and I was happier than ever.
Another one I bought was for 11k on a drop. I also optimized it...sold this one as well @ xxx,xxx.
Okay I hate discussing figures, but you guys should get the point.
Now to answer some of gugushes questions.
1. The category doesn't matter, but I never had any poker, casino, or adult domains. Those are usually good if only parked with services such as Fabulous. I buy domains that will do rather good everywhere.
2. Type-ins are best. For instance....ToyotaLexus.com, or something like that. But I had typos as well.
3. Well there is no good parking service. Most of them take more profits from the domain owner than you can imagine (that's why I am developing my own), but I did use Sedopro, Klickerz, RevenueDirect, Domainsponsor, etc. Also used Google Adsense.
4. I bought it on the forum and optimized it.
5. Well yes, but I am 18 so I don't really have much expenses as of right now. I don't own a house and I don't pay my rent. I view this as a hobby. A big hobby. I also view this as a gambling addiction. Again, a HUGE addiction that I can't get myself out of no matter what I try. I had about 10 domains in my portfolio. But depends what strategy you follow. You can make alot of money with 3 domains or 100,000 domains. It is upto you if you want to follow the path of finding good deals or follow the path of registering typos, or something in the middle.
7. I do not advertise anything. The domains have to receive natural type-in traffic, or typo traffic themselves. Advertising could actually get you banned from parking services, so I'd advise against that for your own good.
To wrap this up, these are basically the things you need to do to make alot of money on the internet. And if you disagree with any one of these, you will probably not have a success on the internet:
1. You must work hard.
2. You must always follow your goal, no matter what. You cannot lose hope.
3. Have 1 good idea that you really want to persue, instead of 500 ideas.
4. Take risks. Big ones.
5. Don't be desperate. And also be patient.
6. Work in silent mode. Don't be a show off. Don't be like: therichjerk.com!

Just like in Scarface:
Scarface said:
" Y'know I told you when you started
Tony, the guys who last in this busi-
ness are guys who fly straight, real
low key, real quiet.. -the guys who
want it all, the chicks and the cham-
pagne and the flash -- they don't last."