Places to be:
The primary way that Rubinius developers communicate with each other is IRC. Yes, we know it is the 21st century now but give it a try. It is even at this late date the best means of communication for a large distributed project. IRC clients are available for any imaginable OS. If it can access the Internet, it has an IRC client. More on IRC, a list of clients and a nick list can be found here. IRC logs are also available.
If you cannot (or prefer not to) use IRC , feel free to ask questions or submit patches via the mailing list as well. The mailing list is relatively quiet currently because of the heavy emphasis on IRC but rest assured, you will find yourself in a discussion on the ML as well if you send the first e-mail.
If you are just starting with Rubinius feel free to ask for help! We try to make sure that there is documentation available and someone will always be able to answer questions all we ask in return is that you bring an inquisitive mind and are willing to do proactively poke around the code or research otherwise also.