I've written about TouchDown for the Google Android a couple of times (here and here) and as I have said in those posts it gets better and better on a regular basis. I have been using beta versions and the latest available beta supports PUSH email, ability to send attachments, device-local drafts, and more. The folks at NitroDesk, Inc. were able to sign a licensing agreement with Microsoft to support direct push capability through Exchange ActiveSync. I think this is one of the first products for the G1 that provides this functionality, even though a couple others are working on it as well.
TouchDown has filled a major void in the Android space for me personally and with the full push functionality and Exchange syncing capability I can now use my G1 as a daily phone if I desire where before it was primarily a hobby phone. At this time, the push functionality is available to those who are signed up the beta versions, but it will be available soon as a free upgrade to the commercial product in the Android Market for all licensed users.
In addition to the push technology, the ActiveSync license includes security related features such as PIN enforcement, prohibiting databases from being placed on the microSD card, and remote wipe capability when used with a server that supports it. These security features may aid in the consideration of the platform by companies concerned about security.