OOohh downloading now! Cant wait. Still judging by the known issues, this is well off, probably end of summer...

Known issues
• 32-bit kernel extensions are not supported in Mountain Lion
• AirPlay mirroring is not supported with the with the current version of the Apple TV software
Game Center
• The Game Center Server environment is set to Sandbox. Existing Sandbox accounts may be used, or you may create a new account
In the Sandbox environment:
• Game & Friend Recommendations are not supported
• Friends can view games in common but not friends' other games
• Photos are not supported
• No email vetting and friend requests to un-vetted email addresses are allowed
• No support for out of network friend requests is provided
• Game matchmaking versioning restrictions are more relaxed
Some of the Game Detail information does not display (Game Provider, Pricing, etc.) in this Developer Preview
Search is not functional
No badges shown for Friend Requests
Peer-to-Peer GameKit API is not supported
Leaderboards, Achievements, or Players may be displayed incorrectly. To resolve this issue quit Game Center and re-launch

• The new Notes application does not currently import the following types of notes:
• Microsoft Exchange
• Notes existing in sub-folders of IMAP accounts
• Local notes in an "On My Mac" account
Notes in these accounts will be available in Mail
• Notes shared via Messages may not include note content
• Screen Sharing may not work between OS X Mountain Lion and Snow Leopard or earlier OS X releases in this Developer Preview
• AppleScript is not fully functional in this Developer Preview
• AppleScripts used to launch Applications which are not already open will time out
• AppleScripts may not be able to send AppleEvents to Mail
• DVD Player may not launch after inserting a DVD on some systems
• DVD Movie Playback does not work on certain NVIDIA GPUs
• Horizontal metrics for Apple SD Gothic Neo are narrower than in AppleGothic. Applications localized to Korean may experience text layout underflow in multi-line text strings
• Video content with displays that use HDCP may experience graphics corruption on certain NVIDIA GPUs
• Enabling display rotation causes kernel panic on certain NVIDIA GPUs
• Signing into Setup Assistant with your AppleID does not sign you into iCloud
• NSDocument-based applications which use auto-save & iCloud entitlements will be opted into the new Document Library automatically. The option to disable this is not currently available
• Kernel, kexts, and zones are now based at unpredictable addresses at each boot. The addresses in the kernel symbol table are unslid, and will not accurately reflect a running system.  Provided that Xcode 4.4 gdb is used, KASLR is transparent to kernel debugging
• To temporarily disable KASLR, set "slide=0" in the boot-args
• Panics may occur when a Port Multiplier or PCI eSATA drive is attached
• While booted into the Recovery Partition, you may be unable to connect to WiFi networks
• Safari does not function in the Recovery Partition
• Restoring from network backups in the Recovery Partition may fail