Apple has just seeded the Gold Master (GM) candidate for OS X 10.7 Lion to developers. That's the desktop jab, scheduled to land this month, that Apple is using to set up the overhand right of iOS 5, which will finish the combo this fall.
What's interesting here is that Apple seems to be distributing Lion by Mac App Store redeem codes for the major milestones, and via Software Update for the smaller releases. By contrast, Apple has stuck with the tried, true, traditional direct download method for iOS 5 beta 1 and beta 2, though with the new over the air (OTA) features built into iOS, it's possible they could try and test that system sometime in the next couple of months.
Lion, like iOS 5, will tie into the also-in-beta iCloud system so developers testing iCloud APIs for iOS will probably want to see how they work in Lion as well.
We probably won't see iOS 5 GM until September, but once and while, new iOS-centric features sneak into the OS X updates as well, so keep your eyes open.