[http://nightly.webkit.org/builds/ Nightly builds] are now available for download.  There are several  [wiki:"Known incompatibilities between open-source WebKit and Safari" known incompatibilities between open-source WebKit and Safari].  Please be aware of these before filing bug reports.

If you are using Saft, you will not be able to run the nightly builds. Removing Saft from /Library/InputManagers will allow you to run the nightly builds.