This free utility that runs on 32 and 64 bit machines has no size limits for image compositing. Although the site says that multiple point perspectives are not currently supported, a geographer from the French equivalent of the USGS says that he has used it to do a multiple view mosaic. The code is NOT opensource, but this could save time IF a community decides that they need the data quickly.
The tool is here: http://research.microsoft.com/en-us/um/redmond/groups/ivm/ice/
If anyone has experience with this, please post as there is nothing on the googlegroup with Microsoft's ICE. I will try this and post results as soon as I get back to the US to a computer with some data sets on it.