On MacOSX 10.8, wx-0.90.0.1, ghc 7.4.1, I tried to run http://code.haskell.org/wxhaskell/samples/wx/FileBrowse.hs but it crashes. When trying various treeCtrl functions in an isolated setting (copying code from the sample) a crash did occur as soon treeCtrlAppendItem was called.
MacOSX crash dump