Apple is seeding yet another build of OS X 10.8.4 to developers, 12E52. As before there are no known issues, and Apple is still asking developers to concentrate testing on Safari, Wi-Fi, and graphics drivers. When it's finished v10.8.4 is primarily expected to be a maintenance update, although it does appear to include
support for 802.11ac Wi-Fi.
That may hint that Apple is on the verge of releasing updated computers, since current Macs only support Wi-Fi standards up to 802.11n. A refresh could take place as soon as June 10th, the start of WWDC. That might also explain the intense pace of v10.8.4's development, which has seen new seeds coming once a week.