Let me document some hiccups, for all those who are planning to do something similar to this.
1. Zon set the price back up to $2.99 automatically. Reason: I'd used the "promotional price" tool on wide sites like itunes, google, and Nook. I set the price to end on June 1, so the price went back to $2.99 on those retailers (except Google. See No. 2.) And 'Zon immediately priced it back up. I admit I was impressed by their speed. I've decided to keep the book free for the summer, since it actually is drumming up sales of the other books. So, I reset the price to zero on itunes and Nook, and 'Zon IMMEDIATELY (as in within a day) set my book price back to free in the U.S. without me asking. International prices didn't go down though, but I lowered them to the equivalent of 99 cents US.
2. Googleplay. My promo price ended, and instead of raising it back to regular list, they delisted the book and it was no longer available. Eek, I didn't realize this until I checked for new downloads last night and there weren't any. They took it off sale on May 31. Ugh. Anyway, I had to go in and redo all the book details, and once I'd done that, the book is now available and free in the store. Didn't see that coming!
Also, the promo has been successful in that it is moving books 2/3. Basically from nothing before the promo to one, two, sometimes three every day. I've earned back about $120 of the $377 I spent so far. I will update with the sales numbers later. Hopefully I will at least break even on this!
Reviews are also a nice surprise. I wasn't expecting them, but they're trickling in, and not just on Amazon. On wide as well.