I've noticed the following issues with the Q3 2011 Beta demos when viewed in IE7.
The DatePicker controls appear to be displaying the date selected overlayed on top of the display text.
The TimePicker control's text input is covering some part of the clock image and it exhibits the same display issue as the DatePicker.
The Notification control's z-index doesn't appear to be high enough to cover other controls when in IE7, but it works in Chrome. The demo is:
http://demos.telerik.com/aspnet-ajax-beta/notification/examples/sizeinpercent/defaultcs.aspx
The RibbonBar Contextual Tabs demo when using the Metro theme does not display the Edit tab correctly (same in Chrome, even worse in Chrome), but it works for the other skins.
Those are just some of the issues I've found with the beta demos. I've attached the images of what I've seen.