OpenSSH 5.1 includes a feature called visual fingerprints for host keys. Before this feature came out, keys were represented by a hexadecimal sequence that you would usually see the first time you log into a host. Now they're also represented by high-tech looking ASCII art.
+--[ DSA 1024]----+ | .o | | ..o | | .o +| | .E* | | S o o .+| | o = B o. o| | o o = o. | | . o . | | . | +-----------------+
Few users would ever bother to remember a host key; because the verification is performed by the SSH client. The user's concern with a host key only comes into play during the first time logging on to a host, or if the key sent from the host doesn't match the expected key.
Visual fingerprints changes the user's process of identification. Instead of having to remember a sequence, they can recognize the pattern of the key. Through continued exposure of the fingerprint, users will become familiar with it, and immediately recognize a problem if the key changes.