For a while we were allowing some players to "merge" or join their accounts together by combining all of their pets/items onto one account and playing on it together. Now we've stopped allowing it.
In the past when we did allow merging, we wanted people to ask admin permission before going ahead with the merge. This is because we wanted to protect players from bad experiences when merging with untrustworthy/unreliable players, and we wanted to prevent people cheating by "merging" with their own extra accounts or by continuing to play on more than one account each.
We turned down requests that we believed might turn out badly, but even with our scrutiny many of the approved merges have turned out badly. Some people either split up after a fight and unhappily lost pets/items as a result, many realized that it was no fun having someone else mess with their pets, some got themselves and their account partner banned, and several tried to steal everything from their account partner by changing the username and password. Of those who didn't get an admin's help to merge, many continued playing on more than one account (keeping a shared account as well as a personal account) and were banned for having multiple accounts.
We're currently not approving any requests for players to merge. We don't believe there are any benefits to merging, yet there are many risks and costs.
For those who have merged before February 2012 - you can continue playing that way. But we're not approving any new merges.
Also an important note for players who thought it would be wise to merge accounts without getting admin approval - if you kept a shared account as well as your own personal account then you may be banned for controlling multiple accounts. Each user is only allowed one account, so no-one has a reason to be using more than one. If you're in this situation, you need to contact an admin immediately to get it sorted out.