A year ago I decided to take a year off from consulting, mainly to spend a lot more time with our kids while they are still young, but also to have some time to explore some product ideas.
After a couple of months of development I finally got it all working.
I had it all working in my initial build environment, which was XP based. Then I tested in Vista, and I couldn't get it to work (the GetProviderProcessData failed). Ouch!
I took a step back, gave the product a long hard look, and decided to stop development. It was too slow (despite being entirely in-process), I couldn't implement features I needed such as timing (the debugging/tracing added too much overhead), and I couldn't get it working on Vista.
Now that IE8 has similar profiling features I'm happy I stopped when I did.
If there is one sure way to kill a product idea it is to register domain names before you've executed on the product idea itself :-).