The Wikipedia article says Webkit is based on the HTML rendering engine Konquerer uses (KHTML) and now included in Qt version 4.something even though konquerer still uses its own branch of KHTML. Webkit is ported to Gtk and some projects startet to include it. (click list here
An "embedded" version is available - for example for Nokia S60 based cell phones (the ones which also support the Python development API, btw.), but OpenMoko also ("the open source cell phone") seems to use it.
Webkit compiles perfectly fine (at least under my Slackware 12) from source, so you just can try out and see for yourself. The source isn't specifically marked as "download linux stuff here", but it compiles and people use it to experiment.
If you really want details, check the comparison tables listed in the Gecko Layout Engine article of Wikipedia, they're most helpful.
Rendering Engine Comparison
(See "see also"