Printing is broken on gimp-2.4.0_rc1. The normal File > Print doesn't do anything (i.e. the "Print" dialog doesn't even appear), File > Print with Gutenprint opens the gimp-print/gutenprint (using version 5.1.2) dialog, but it is unusable ( the paper size, image size, marginals etc. are set to 0, and changing them doesn't seem to affect anything) Everything worked fine with gimp-2.3.19 and earlier versions.
Fixed in _rc2.