Some news about new functionality in "extract.exe".
Now you can use option "-filter=ClassName" to enable extraction of the specified classes only. Class names are case-insensitive, plus you may use a few "filter" options. Examples:
extract.exe -filter=TextBuffer C:\GAMES\UT3\UTGame\CookedPC\Engine.u
extract TextBuffer objects only (script source)
extract.exe -filter=skeletalmesh -filter=animsequence C:\GAMES\UT3\UTGame\CookedPC\Characters\CH_AnimHuman.upk
extract SkeletalMesh and AnimSequence objects only.