My personal rules for this are: 1. If I haven't used the domain in 2 years, it's never going to happen so I will let it lapse That in itself may not be enough

My personal rules for this are: 1. If I haven't used the domain in 2 years, it's never going to happen so I will let it lapse That in itself may not be enough, as you may become attached to some of the names, because they're just too good. So there is also rule 2: 2. Max 12 domains at any time (1 for each month), to keep costs reasonable. If I'm at 12 domains, and I have a really good idea for another one... I have to weigh it against the existing domains and either not register it -- or immediately turn off auto renew for whichever other domain lost against my brilliant new idea.