tweetymail takes a different approach in trying to reduce your need to visit the Twitter homepage or yet another Air client. You simply associate an email account with them (and their oAuth login) and off you go.
You can send emails in to create the tweet, follow someone or even send links. They have a good example of sending the link as email right from your mobile or any desktop browser. Instead of you sending email to some coded address only you know, they reverse it and look for your configured from address.
This is good and bad. The good is that you don’t need to create address book entries or try to remember it. You can then tweet from anywhere you send as your email. The bad is you have to use your email to send it always, instead of to the code and it is slightly possible that someone could send as you if they knew you used the service.
While they are trying to use SPF, DomainKeys and other measures to verify the sending server, it is not 100%, but is ok.
Tweetymail will automatically shorten URL’s (I didn’t see where to configure which shortening service to use) and they will ignore your email signature.