I thought I had a lot at 6 domains. I'm surprised to see people own hundreds of domain names. It seems like it would be nearly impossible to provide good content and build links for that many sites, unless you have many people working "for" you to do the work.
I think developing domains, at least in long lasting content areas, is much like planting seeds of slow growing trees such as oaks or olives. Register the domain today, put up some on topic placeholder content and point a few links to it. Add a page every couple of months. In a year or two it might be worth working on for real. I also find that I have registered names which I thought would be interesting but for which I had no idea of how to profit from. A year or two goes by, someone comes out with a new ad program and/or piece of software and suddenly there is an opportunity. That's when you will be really glad you have some of those little "trees" started How's that for rationalizing more domain registrations
4 months back i was satisfying myself with .tk domains. now I have 16 domains of which 4 are in developing stage. Off Remaing 12, I think I will develop atleast 6 as and when i get time.
I have hundresds of them com, net, org, biz, ws, info, name, co.uk, org.uk, and us most of them parked though