Ableton announced that Live 5.2 upgrade is now available. You can get it from the Abledton Live 5.2 Upgrade Page. If you need to purchase Live, go here.
According to Ableton's press release on this, 5.2 adds support for native Intel-Mac making Live 5.2 one of the first professional audio applications on the market to run as a "Universal Binary to take advantage of Apple's fastest machines: the new Intel-Mac". The release offers bug-fixes for Intel users.
I'm on Intel and I upgraded last night without any problems. Sets created with Live 5.0.3 loaded and played back as expected.
Below is an excerpt from the Ableton's web site with more details on the upgrade:
Live 5.2 is available today, bringing immediate native Intel-Mac support. This development makes Live 5.2 one of the first professional audio applications on the market to run as a Universal Binary to take advantage of Apple's fastest machines: the new Intel-Mac.
Intel-Mac users: Intel-Mac users can purchase a new Live 5.2 serial number for 49 USD/39 EUR via the Ableton webshop. Customers who purchase the upgrade to Live 6 from the Ableton webshop will receive a full refund of this 49 USD/39 EUR. Live 6 is scheduled for release in Q3. Complete information on Live 6's specs, availability, and pricing will be made available this summer.
Accommodation for recent buyers of Live 5: Users who purchased Live 5 after Steve Jobs' announcement of the new Intel-Macs (January 10, 2006) will receive the Intel-Mac Live 5.2 download at no additional charge.
Non Intel-Mac users: For Live 5 users on PCs and non Intel-Mac machines, Live 5.2 is also available as a free bug-fix update here.