For the 2.6.x branch (trunk) arcsde raster support has been completely refurbished in order to support all the ArcSDE raster pixel depths, and any number of bands (with the exception of 4-bit rasters and 1-bit ones with more than one band), as well as colormapped rasters (8 or 16-bit rasters with a color pallete).
The vector support was also enhanced to perform really well under high concurrency.
All the changes in the 2.6.x series are being backported to the stable 2.5.x branch.
For the 2.5.x branch arcsde has been almost completely rewritten, it no longer extends AbstractDatatore and the code is much easier to follow. Internally it protects all SeConnection use behind a Queue (rather than a Lock) as a way of addressing concurrent usage in a fair manner.
Also, it has been extended to support the read and edition of versioned tables, limited to edit the default version.