A blog entry I read recently points out that Apple's WebKit (or at least the OS X version of it) contains various closed-source and binary only pieces of code that make use of Mac OS X internals. This is, by itself, morally dubious and not really compatible with the idea of open source. However, it may also be a violation of the LGPL.
While the LGPL allows closed source software to make use of the library, it still requires that the whole of any modified version of the library is distributed under the LGPL. It would appear that WebKit is violating this requirement by keeping parts of its code closed-source. (Of course, since WebKit is based on the LGPL-licensed KHTML, which Apple don't own the copyright to, they can't relicense it under more favourable terms.)