We do (and we couldn’t prevent it anyway, even if we wanted). However, what we do not allow is using multiple accounts to perpetrate fraud.

We don’t have any problem if you want to have different accounts to post in /c/politics, /c/trolls, and /c/sex/MyBedroomToys. We get that a different persona might be required (or, at least fun to use – heck, just look at SecondLife). We also don’t have a problem if you post something and then openly upvote your own content once. (That’s called self-promotion and it costs you one karma to do so.) And if you want to create a few accounts to test how certain functionality works and throw a few karma around, knock yourself out.

What we do have a problem with is someone who creates multiple accounts to discretely self-promote and earn karma by making it look like many others are upvoting, or someone who moves karma around to obfuscate transactions. If we find you doing either, especially or primarily in an effort to increase or redeem your karma, all of your accounts will be immediately deactivated and you will lose all of your karma. In other words, while we’re very supportive of communities like /c/gaming, we don’t want you gaming the system. We have a high regard for trust. Don’t break ours.