Another new feature developed during the Google Summer of Code 2008 coming to Hugin in the future: an advanced mask editor.
In panorama stitching, overlapping images are stichted together to a single image. Because they are taken at (usually) slightly different points in time, there may be movement between them. The traditional way to deal with movement is to have enough overlap covering the area and then masking out manually and painfully, in the Gimp or in Photoshop, the areas concerned.
Masks can be useful in many stages of the process: at the stage of control points (CP) detection they are useful to tell good areas apart from bad areas. CPs further away suffer of less parallax than CPs at close distance, and at the blending stage they can help decide which of the overlapping images should be retained in the final panorama.
Like many new functionalities, this questions the current workflow model and the related GUI in Hugin, which has already been stretched from its initial design for the inclusion of photometric adjustment and the processing of image stacks. It is likely that more work is needed before this feature will hit your desktop.
Maybe not for the next release, but it is in the pipeline.