As a software developer and web enthusiast I have one or the other domain in my possession. But it always bothered me that "this one great domain" is already taken. So I hooked up to a bunch of APIs and built an interface that not only lets me manage my domains, but also lets me monitor domains that are already taken.
If I put such domains on the "watchlist", the status is queried at regular intervals. As soon as the domain changes to a relevant status (about to expire, cancelled, available for purchase on the free market), I am informed via push notification / SMS / email.