As an early user of Chimera/Camino, Phoenix/Firefox and Safari, the way I recall it was that KHTML was too good at standards, hence causing practical problems with actual web content which was built for IE. (A big part of Mozilla's energy at that time was in evangelizing websites to actually use standards and not block them for no reason, but they'd also done a lot of reverse engineering)

I also vaguely remember David Hyatt saying that they (edit: and by they I mean the Safari team that he'd moved from Mozilla to join) had taken some component from Gecko though I can't remember the details and his old Surfin Safari blog at http://weblogs.mozillazine.org/hyatt seems to have been superceded by the Webkit team's Surfin' Safari blog and it now just gives a broken redirect.

I remember using Konqueror and I always liked how fast it was. Indeed, many websites had problems when rendered with KHTML, but all that was needed was some polish.