In Europe at the beginning of March 4-Core and 8-Core systems were available for immediate dispatch, now dispatch is listed at 3-days on all models except server, which is 1-3 days. This week in Japan 12-Core model has slipped from 3-days to 5-7 days, and in the last couple of days the 4-Core and 8-Core models have slipped from immediate dispatch to 1-2 days. Apple probably originally planned to update last Summer / Early Autumn, with AMD 68xx GPU. The 10.7.3 Lion update had drivers fro the AMD 79xx series (Tahiti) so Apple have almost certainly been testing them. Given that the GPUs are 2 generations out of date an April update before the Intel Ivy Bridge launch on 29th April seems likely.