I started buying domain names in Jan 1999 when I was still doing a sensible 9-5 job. I quit the job in mid 2000 and have been flying under my own steam since then (but not all domaining).

Anyway, back to the subject in question - there are now over 4,000 domains in my portfolio, over 3,500 or which are .com. The rest are .net, .org and .co.uk, and oh yeah, I bought one .me in a fit of madness.

I sell around 1 or 2 domains per month, and the rest are parked across the major parking companies - Sedo, Namedrive, Fabulous and Parked.com. 

At the minute I'm mostly investing in IDN domain names, as I feel that they're the least understood by the general market, so at the minute they present the biggest opportunities for domainers - it also helps that expiring IDN domains do not feature on Namejet, Pool, Snapnames and the like - so finding good expiring IDNs requires a little bit of specialist knowledge and there are not that many people doing it - in some ways it's similar to the situation in 2001 to 2003 when good English domains were expiring and being picked up for reg fee by the likes of Frank Schilling and Yun Ye.

Many of my domains are single word generic domains or Geo placenames. To see a few examples of my domains have a look through the different portfolios below:
 

English Generic     Spanish Generic 

Spanish Geo     Spanish Medical