I'd like to share my attempt at the Sencha Touch Contest (Which did not make it to the top 10)
What I have is an email application with multiple account support, contacts and signatures.
All pretty standard, until you get to the inner workings.
It's all based around WebDatabase and have the corresponding Store and Proxy extensions that translate your database to record models inside the store and back. All methods are supported (you write to the store and it writes to the database)
sorting and filtering is also on. Still working on the paging integration.
The application itself uses a php backend to proxy all the information to and from the IMAP/SMTP servers. Nothing is really kept on the server. There is no database or anything, just the source files.
More about it you can find at TouchMail