As of April 2009, I decided to discontinue the development of ActiveRecord::MultiConditions to concentrate my efforts on other projects.
If you are looking for a good alternative, I encourage you to have a look at Ben Johnson's Searchlogic library. SearchLogic provides all ActiveRecord::Multiconditions features along with many other cool stuff.
There are many other projects that needs my assistance at the moment. I'm planning to release a new version of Tabs On Rails with multiple tabs support and I'm working on a couple of Rails products.