The Groovy team has kicked out their second major production release, Groovy 1.5...and skipped straight from 1.0 to 1.5. Why? Perhaps because they added generics, enums, static imports, annotations, fully dynamic metaclasses, improved performance, ... and much more. I think the move to 1.5 was certainly warranted, and we've been considering making the next JRuby release 1.5 for the same reasons.
Congratulations to the Groovy team! I'm looking forward to seeing 1.6 and 2.0 in the future!