You'll need libc++ from clang since system libstdc++ lacks support for C++11 and later. Don't bother following the build instructions in the wiki. You should instead just get a subversion checkout of Safari-604.3.4 as described in the wiki. You'll also need git in order to apply the patch I'll hopefully upload soon.
This seems to be [#115]. You should get previews working by using a relinked Safari application instead of the WebKit application. Make sure your system is as idle as possible, drag your Safari application and drop it over the "Relink against Leopard WebKit" droplet that comes with Leopard WebKit. Then wait until the doplet's icon disappears from the Dock - you should not use your Mac while the droplet is doing its work, as it may fail then.
Well, unfortunately the automatic update messages don't work for Leopard WebKit - they work (or at least used to work) for Apple's WebKit releases exclusively. I just used their WebKit application (a Safari launcher in fact) as it was when they released it for 10.5 for the last time. You need to check the Leopard WebKit project web site in order to know when there are updates. All in all Leopard WebKit is not very convenient for the average user who doesn't care of the inner workings of applications...
Link from history missing when going back one page
I know that behavior - but I haven't investigated yet whether it's a bug or intended like this.
As WebKit largely depends on C++11/14/17 features you'd need to use a later version of clang. David used clang-3.8.1 and that proved to work. But be warned; it'll take some weeks until the first completed build. In case you seriously consider doing the build, I'll post the results of David's work here - and we got pretty far. And you need to keep in mind that you can't use Safari 5.1; browser options to be considered are Safari 5.0.5, Roccat and Stainless.
As WebKit largely depends on C++11/14/17 features you'd need to use a later version of clang. David used clang-3.8.1 and that proved to work. But be warned; it'll take some weeks until the first completed build. In case you seriously consider doing the build, I'll post the results of David's work here - and we got pretty far.
This is indeed because of Growl - it can't deal with being invoked by certain background tools like "Safari Webpage Preview Fetcher". I found a workaround and will either release it in a last 603 version or in the upcoming 604 series. A relinked Safari will not cause that problem - for now I'd recommend to either disable preview rendering using the supplied script or using a relinked Safari application.