Has anyone solved the public web site username problem?

The problem is that in most instances individual users of a web site require a unique username to link them and their transactions. The general public will typically try and use all or part of their actual name as this is easy to remember. This results in multiple "collisions" around common names which are often resolved by sites suggesting an alternative with a numeric suffix. This feels inherently insecure to me as it exposes the existence of one (or a sequence) of pre-existing user names and let’s face it many users will chose insecure passwords. Some sites work around the problem by using an email address as a username (which one would trust was unique) but this potentially makes changing a contact email address more complex than it should be and makes the "tagging" of data items shared by small groups more complex (yeah - I know that partly undermines my first paragraph). Are the OpenID options the solution as they (at least) do not expose individual site usernames? If so - which have you found the best to work with?