You can use it to your advantage too. Start your IDs off at a big number, and your first few savvy customers that see their ID think you're a lot bigger than you really are.
So instead of knowing they're user #8, they think they're user #14221, and are a lot more likely to trust you with their money.
It works well for throwing off the competition too. "Holy Crap! They have 150k users and they're only 3 months old! We're screwed!!!"