Putty remember username
Solution 1:
You can simply save the host or ip address field in putty as ubuntu@ipaddr.
Solution 2:
The option to enter a username is somewhat hidden in the Connection --> Data tab.
You can save a username in either your default profile or for a specific session.
Also of interest: the suggestions from http://dag.wiee.rs/blog/content/improving-putty-settings-on-windows