I use this for internal items, as in: real customer IDs start at 10,000, so we have 9,999 possible users/invoices/whatever for our own usage in the database. Th

I use this for internal items, as in: real customer IDs start at 10,000, so we have 9,999 possible users/invoices/whatever for our own usage in the database. That makes it easy to filter demo accounts of your sales employees, or production test accounts, in queries: just add an offset. Re: the upper bound: if you reach a million customers, you have lots of other nice problems, like how to spend all the money they earn you :-)