On April 8 Intel will announce Z77, Z75, H77 and B75 chipsets. On the same day we should see numerous reviews of 75 and 77 boards with, well, Sandy Bridge CPUs.
Ivy Bridge processors will be announced in the 4th week of April, between April 22 and April 28. The announcement will include only quad-core models: mobile Core i7 and Core i7 Extreme families, desktop Core i7, Core i5-3570K, i5-3570T, i5-3550, i5-3550S, i5-3450 and i5-3450S. The announced chips will be available for sale on April 29, and the reviews and benchmarks should be published on the same day.
Apple has reportedly already begun production of new thinner 13 and 15-inch MacBook Pros which are thought to utilize Intel's Ivy Bridge processors.