The subsites module is probably what you are looking for. You can use the 1 CMS to manage multiple sites. For a real world example we have recently done is the epmu.org.nz site. This site uses the subsites module to control the http://www.workrights.org.nz/. You can also create, manage as many subsites as you want and set custom themes.
As to the state of it for 'general' release, It has no documentation and has had no public releases as of yet (only used on a few internally done sites) so its probably in the 'risky' to use category!