Yes and no : Since we're probably going to want to support different archs coming from different build machines some day, the build spawning should be per build host, whereas the dealing with the results will be partly per build host (the part that you consider fairly related) but also partly in a central location which will gather everything, right?
Other than that, I agree with Jeremy regarding the fact the builds should be explicitly requested and not automatic for every CVS commit, or even every commit matching certain criterias (i.e. a change in version and/or release).