One of the main differences in IE7 is the way modal dialogs are implemented. For example: in all the dialogs is the addressbar displayed. It’s launched in another way(it goes trough a different security pipeline). Mostly it has the same properties a popup. But.. there’s more! You can resize them without any problem and last but not least, you never got that problem again that everything is locked because there’s a hidden modal dialog. IE7 will change the tabicon. For more information about modal dialogs click here.
The publishing dialog of Sitecore 5.1.1.11
By the way, the IE-team does give feedback in chatsessions. You can find the shedule of those chats here. Can we do those sessions with Ole and Runi for Sitecore too…? 
SDN5 isn’t right rendered by IE7. I guess Alexey Rusakov has made SDN5 and he should shame himself! 
I found this in their HTML:
Now my searchbox in IE7 looks like this?!
Only 1 line of the box appears
Actually I was so ashamed that I had to go on a sick-leave for two days
Thanks for the tip Alex.