Matt Chotin (the Flex SDK product manager at Adobe) just posted to say that http://www.adobe.com/cfusion/entitlement/index.cfm?e=flex3sdk has been updated for the new v3.4 SDK.
That page also has the Data Vis. components listed, and the download includes the source and is no longer watermarked.
Previously a Flex Builder licence was required to obtain the source and remove the watermark.
Update 28th August 2009: Matt talks more about what's happening with the Data Visualization stuff here, including exactly how 'open' they really are.