In the progress of processing Bugs in SubEthaEdit I found out a serious memory leak in the WebKit/Safari.
E.g. this blog triggers it (actually that was how I reproduced the leak accidentally while designing the layout of this blog in SubEthaEdit), but I put the gist into leak01.html
Just load the page, open up a terminal with top, watch RPRVT of Safari, then press reload often. Memory rises quite quickly. It apparently has to do with background-images that are assigned via css. Looking into it with MallocDebug showed that an awful lot of Memory gets allocated while redrawing and generating the corresponding Pattern. Hope this helps.
Thanks to Jon Nykänen for pointing me to it.