Just downloaded the latest Beta of the Debug Bar!  I thought I would offer up some suggestions on improvements.

1.) The attributes in the Source tab, should reflect the REAL source, not the <xmp> IE Source.  Not only does it return incorrect tags, quoteless attributes etc. but there are some issues with it returning the correct node structure too.

2.) Ditto with the CSS tab, I've never set a 'BORDER-RIGHT' property in CSS ever... yet the style tab is littered with these UPPERCASE tags.

3.) Tab contents... tend to vanish if you have ANY iframe contents that refresh (META), thus if you navigate to a certain element, you need to read it before the next refresh (this includes navigating to any content not in the iframe.

4.) I would (if you can) place the drag target icon on the right (e.g. align-right) of the sidebar... since it is frequently used, and users will want to have it handy.

5.) The Run JavaScript button on the Script Tab gets cropped top/bottom... I would also recommend not setting the width as 100% as it only makes it look real cheesy because of the IE button stretching bug in XP

6.) The Email Screenshot feature (which sounds great) is Hard Coded to use Outlook.  Since I don't use Outlook, like 1,000s of others, this feature will be broken for many developers.

7.) After playing with the zoom feature (and the debug bar sidebar closed), if you reset the zoom to 100%, then click the button to open the sidebar, IE crashes.

8.) Some sort of Outline feature would be very handy (e.g. outline Table cells)

Otherwise, still a million times better than the MS IE Developer Toolbar.