I use a clever program that I downloaded which will take care of most of the PG text problems. It's called "GutenMark" and comes from http://www.sandroid.org/GutenMark
GutenMark outputs HTML or LaTeX. After converting the text file to HTML with GutenMark, I then follow HarryT's directions for using BookDesigner and then MobiPocket creator to create MobiPocket books. Next, I use Calibre to create the Sony BBeB format and ePub. Lastly, I feed the MobiPocket book into Mobi2IMP and create the .imp formats.
If I'm going to be converting a book for my own purposes, I go ahead and create all the formats and upload here. I figure someone else might be interested.
Update: I missed Patricia's mention of GutenMark. Sorry.