Jesse from Hog Bay Software (who created WriteRoom and TaskPaper) informs me that PlainText for the iPad and iPhone is now available (for free) from the app store:
It's a beautiful-looking text editor, but the really cool thing is that it syncs with Dropbox. This means that it can be used with the upcoming Scrivener 2.0's "Sync with External Folder" feature, which is an alternative to the Simplenote syncing. So you will be able to sync documents from a Scrivener project with your iPad or iPhone, edit them (or create new ones) in PlainText, and then bring your changes back into Scrivener when you return to your computer. (There are other text editors coming out for the iPad that use Dropbox sync, too, many of which will also work with this Scrivener 2.0 feature.)
Anyway, congratulations to Jesse on getting PlainText out - it looks and feels great, and I think a good number of Scrivener users with an iPad will find it an invaluable way of editing documents on the go.