Safari 2.0.x for Mac OS X 10.4 (Tiger) or a 10.4.x update should work correctly with locally-built versions of WebKit in nearly all ways. Ideally there would be no incompatibilities at all, but occasionally it is necessary to introduce an incompatibility so that WebKit can evolve without amassing globs of special-case backwards-compatibility code that will be unneeded in released versions of WebKit.
This page is intended to list all of the deliberate incompatibilities between using Safari 2.0.x in Tiger and a locally-built version of WebKit. It might also mention incompatibilities between the latest Safari 3 beta (Tiger or Windows) and the latest WebKit. If you know of any other incompatibilities, then either this page needs updating or (more likely) they are unintentional bugs. Please use http://bugs.webkit.org/ to report such bugs.
The following incompatibilities exist in all publicly released versions of Safari
Site icon support seems flaky or intermittent
Recent changes to the icon database have moved it towards a fully asynchronous model where all access to the disk occurs on a background thread. It was necessary to make use of notifications to alert the browser that an icon has been received from network or the disk. Safari 2.0.4 (Tiger) and the current Safari 3 beta (Tiger or Windows) do not listen for all of these notifications and therefore site icons will seem to work poorly in Bookmarks, History, and the location field.
Problems running two WebKits after r25439
r25439 changed the format of the icon database on-disk to be more flexible and performant. As a result, running a newer version at the same time as an older version will cause conflicts that may result in icons going missing. Additionally if you are a developer running a debug build there are many ASSERTs you might see due to failed database operations. See http://bugs.webkit.org/show_bug.cgi?id=15185 for a more technical discussion.
The following incompatibilities exist in Safari 3.0.4 for Windows (fixed in Safari 3.1)
RSS Feeds do not load with CFURLErrorDomain:305 error
There is a known compatibility issue between WebKit nightly build r27786 (and later) and Safari 3.0.4 for Windows that will cause feed:// URLs not to load with a CFURLErrorDomain:305 error. See http://bugs.webkit.org/show_bug.cgi?id=16147 for the original bug report.
Safari 3.0.3 beta is available at http://www.apple.com/safari/ that resolves the following issues
Forms auto-fill doesn't work
Forms auto-fill in Safari 2.0.x on Tiger is entirely disabled with a locally-built version of WebKit. This was necessary in order to rewrite the form control code in WebKit to not rely on using NSViews.
Clicking on links in content-editable divs loads the link
Editing-related context menu items don't show up
As noted in Bug 12761 Comment #3, contextual menu items related to editing will not show up with Safari 2.0.x in Tiger when used with WebKit nightlies.