for a while I have blocked guests registration buy using one system guest account, i have created, for all guests, meaning shooing cart items are not saved.
2 days ago with the new release, I got back to the original system and got in 2 days around 10,000 guest account.
I find it very annoying that the customer Id increases by thousands for every new customer.
My suggestion is to create a new entity called Guest (a slim version of customers) and migrate from there on registration