Here's a very weird bug I stumbled upon:
In OS X v10.8.1 (I would guess it affects 10.8.0 too), when sandboxed, WebKit sometimes reports plain NSURLResponse objects from web pages where you'd instead expect HTTP ones. For some pages — like apple.com! — it makes them load wrong in the WebView. Non-sandboxed, all is hunky-dory. Seems to have been fixed in 10.8.2 thankfully.