I've just spent the last 3 hours trying to make our new "Welcome to Sampa" message look just a tad similar in Outlook 2007, Hotmail and GMail. Each email application/service renders HTML a little bit different, but enough to make you crazy.
GMail is more aggressive at removing some of the styles that you applied to your email, while Hotmail and Outlook 2007 have really poort HTML 4.0 compliance.
And don't even get me started on Entourage for Mac. Another nightmare.
I'm the Co-founder & CTO of 
