As this was reported twice in the space of a week internally, I figured that external users may be hitting this too. The internal emails were along the lines of "I added my custom types to autoexp.dat and they don't work". In both cases this was because they were added at the end of the file, but if you look carefully at the 2K5 default version of the file the end is in the [Visualizer] section: auto expand rules need to be in the [AutoExpand] section.
There are close to no official docs on this file, sorry, that was kind of my fault. If VS-next still doesn't have any docs, it will be someone else's fault.