Single or Multiple Instances for different groups

We have multiple groups wanting to use Omeka. Are people using a single instance that is used across multiple groups or are people running multiple instances - one for each group?

What are the benefits/costs of single or multiple instances?

The main thing I see with one instance for multiple groups is the usability of browsing and managing items decreases as more groups add items. The up side is that groups can reuse items and reduce duplicate work.

I read that running multiple instances with one database might be the best option. Is this what is advised?

Thanks in advance.

We don't really have a recommendation as to whether you use multiple instances or a single instance for each group. As you mentioned, if data sharing is important, you'll probably want to have a single instance shared between multiple people.

The downside is that that single instance runs the same public theme for all your users (though can run different exhibit themes for different exhibits, which sounds like what you want).

On the other hand, with Omeka 1.0 there will be a set of plugins for importing existin data (through CSV and OAI-PMH specifically), so sharing data amongst separate installations might not be such a problem in that situation.