I used to be awful at buying domains at the drop of a hat. If I had any sort of idea whatsoever I'd run to namecheap and buy a domain straight away! Phew. And then not do any work on it.
I currently own 25 domains and I use or have used 7 of them.
I'm getting a lot better now at letting domains expire if I haven't used them. Definitely put domains you are using on autorenew but don't do that until you've launched something or have traction.
Can anyone top 25?