Just as another data point, I can ssh fine from Ubuntu 11.10 and Ubuntu 12.04 to ssh servers running on CentOS 5 (OpenSSH 4.3) and CentOS 6 (OpenSSH 5.3).
Just as another data point, I can ssh fine from Ubuntu 11.10 and Ubuntu 12.04 to ssh servers running on CentOS 5 (OpenSSH 4.3) and CentOS 6 (OpenSSH 5.3).