The shapefile module seen a vast improvement in quality, particularly with regards to index support and interactive editing.
This branch is still actively patched for uDig 1.1.x series.
Shapefile index extension was folded back into the core plugin.
A single ShapefileDataStoreFactorySPI was made that will create either a ShapefileDataStore or IndexedShapefileDataStore as the occasion requires.
This release has a known fatal deadlock when editing.
The shapefile code was rewritten to hide all file access behind a single read/write lock - fixing the fatal deadlock above.
Duplicate code removed (between ShapefileDataStore and IndexedShapefileDataStore)
Some Attribute index code was donated, although it has not been folded in yet.
We really want feedback on this one!
The shapefile module is stable, we could use some help supporting attribute indexs.