I've created a greasemonkey script that allows to use current version of GMail for iPhone on a tablet. It avoids shrinking width to 320px and proportionally scales all elements. Also it scales iPhone version of Google Reader.

Screenshot:


I already switched from standard GMail interface to the iPhone version, it works very nicely.

How to install:

1. If you don't have Greasemonkey installed - get it from here
2. Install "Better Google for iPhone v2" script from userscripts.org
3. Open iPhone version of GMail on your browser. No need to change useragent, you can just use special links: for GMail - http://mail.google.com/mail/x/gdlakb-/gp/, for Google Reader - http://www.google.com/reader/i/
4. Enjoy

UPDATE
For those of you, who doesn't want font scaling in GMail and Reader I created a basic version of the script, which only avoids shrinking of GMail window and removes a Google Reader logo.
Install basic version of Better Google for iPhone v2.