From the 30th of January the number of OpenId users will triple to 368 million thanks to Yahoo’s launch of an OpenId service.

Yahoo! Inc. – Press Release via kwout

This makes signing up for services and communities that much easier, simply a login, no need to bother with double opt in emails or miss-typed (unreadable) Captchas.

But what effect will this have?

Remove barriers and actions become more likely.

Facebook applications illustrate this wonderfully. Sign-up is so easy that profiles have become immensely crowded. So crowded, in fact, that Facebook have released a cleaning tool to tidy things up.

Facebook Developers News via kwout

Active Facebook use is dominated by a small core of applications with the majority having less than 2% of their users active on any day.

Good News, Bad News about Facebook Application Market: Long Tail Rules via kwout

Many users, few of whom are active. The same pattern might well be seen throughout the web as OpenID removes the effort needed to participate. We could see more ad-hoc use as people log in, use once, and vanish for months or perhaps for ever.

Potential issues include:

• how to structure communities and directories when the majority of members are in the very long tail
• what expectations users have about data storage without participation
• where and whether an application needs to store user profile data at all

With a long tails of users storage becomes more of an issue, particularly when they expect to bring their data with them.

Drop.io already has an interface for expiring data.

Drop.io: Simple Private Exchange via kwout

Smaller sites and communities running on shared hosts with OpenId enabled Drupal or Joomla installations could well feel an effect with abandoned member profiles gathering dust and clogging interfaces.