The problem I have is that I have multiple accounts with git hosting suppliers (github and bitbucket) but they both want to keep a one to one relationship between users and ssh keys.
For both accounts I am separating work and personal repositories.
In the past I have authorised all my identities on all my repositories, this has resulted in multiple identities being used within one repository which makes the statistics look a mess.
Generate an ssh key for your identity and store it in a named file for example ~/.ssh/id_rsa_timp.
Add the key to your github or bitbucket account.
Use an ssh config file ~/.ssh/config
You should now be good to go:
git clone firstname.lastname@example.org:timp/project.git
url = email@example.com:timp/wiki.git
fetch = +refs/heads/*:refs/remotes/bitbucket/*