I just installed a beta of Mango for WP7 last night and I found a very weird/cool feature for it but I'm not sure if it's from older versions or from Mango.
The feature is that the phone will actually have a data connection when it's attached to the computer while the Zune program is on. I know that it's not using wifi or my mobile data connection because wifi is off and I don't have a sim card inserted in the phone.
I'll post about my impressions of WP7 Mango next week when I'm back in at home.