I founded my first company almost 20 years ago, and haven't been able to stop since. Of my eight startups, four with good exits, I'm usually remembered for the first (one of Australia's original ISPs, Magna Data) or the largest (intertouch, acquired by NTT DoCoMo for A$100M), but my favourite was HiFinity, which made no money at all.
When I started, I was interested in infrastructure, because back then that was where the real need was. Since then though I've been gradually moving further and further towards services, particularly consumer services, because now that the infrastructure is in place, that's where the interesting opportunities lie.
I'm a product guy, an engineer by trade, though I only write code for fun these days. I believe in iteration and customer development and product/market fit and metrics and finding the one thing you do better than anyone else. I also believe in being brutally honest with yourself, and that a startup's job is to create something that materially improves quality of life.