Apple has officially flipped the switch on its next major update to OS X: version 10.7, codenamed Lion, is now available from the Mac App Store as an upgrade to Mac OS X version 10.6 Snow Leopard -- you'll need to have version 10.6.8 installed on your machine. The eighth major OS X release brings more than new 250 features and 3,000 developer APIs, including new auto-save and application restore abilities, plus a few others we detailed here.

The 4GB download will set you back a mere $30 and it can be installed on multiple Macs associated with one iTunes account. It requires an Intel-based Mac with a Core 2 Duo, i3, i5, i7 or Xeon processor and 2GB of RAM. Mac OS X Lion will ship on all new Macs, including the new versions of the 11" and 13" MacBook Air being released today, and will be available at no additional charge to all customers who purchased a qualifying new Mac system from Apple or an authorized reseller on or after June 6, 2011 -- provided they request the upgrade within 30 days of their purchase.

As mentioned above, the company also refreshed its thin-and-light MacBook Air lineup, adding Thunderbolt and Intel's latest Sandy Bridge processors to the mix, as expected, as well as backlit keyboards on all models.

The 11-inch model is available in two configurations: one with a 1.6GHz Intel Core i5-2467M processor, 2GB of memory, 64GB of flash storage for a suggested retail price of $999, and one with double the RAM and flash storage for $1,199.

Meanwhile, the 13-inch MacBook Air models get a 1.7GHz Intel Core i7-2637M processor, 4GB of RAM, and either 128GB or 256GB of flash storage for $1,299 or $1,599, respectively. Configure to order options include a 1.8 GHz Core i7-2677M processor and additional flash storage, but unfortunately no discrete graphics, only the built-in HD 3000 from Intel.