It could help a team to manage a coding convention. Should be very useful in Open Source environments. For example, when committing changes to castle project (or sending a patch) there is a coding standard than needs to be followed. Regionerate could help a lot with that effort.
I need to see if it can select methods and properties by attributes. It could then help making MonoRail controllers and ActiveRecord decorated classes more readable (region of all actions with a "SkipFilterAttribute", region of "Property" and region of "HasMany", etc.)
Silly me, I forgot to mention that I found about this great tool at Roy Osherov's blog. A very good one, that is. Many Agile related stuff, and funny little things, too. So go on and subscribe to it's feed.