There is a "Morph Target" option in the import dialog which says that selecting it preserves vertex and face order, so you'll definitely want to use that (this is new in 2.44) and the same for export.

To load Posette, you'll need to make the edit mentioned (use a copy of course).

No problems loading David ("blDavid.obj"), but you'll more than likely want to unselect material groups in the import settings.

If your exporting just V4's head, you should have just one group, if your exporting the eyes, then you should have three, if your including the teeth and tongue, you'll have several more (again unselect material group on import).
The only option that should be checked on export from Poser is "Include existing groups in polygon groups".

Precision problems caused by the natural size of Poser objects can be avoided by scaling the OBJ (up before import, down after export) using OBJAction Scaler (see FreeStuff) or possibly inside Blender itself; 10 or 100 are probably the best values to try.
Even differences in the last decimal place are noticeable when the morph is applied.