Rated 4 out of 5 stars

This tool provides great way to see what a site looks like when the user has a given size of screen and the browser configured a given way (e.g. number of toolbars and such nonsense)

Things I'd like to see added.
1) better list of standard defaults based on what is in common use including sizes of common tablets in portrait and landscape
2) option of a 'label' on a resolution, helpful to remind you why you care.. Display in the list when choosing, but not once chosen.
e.g. a portion of the default list might look like this
768 x 1024 ipad -portrait
768 x 1366 surface -portrait
800 x 1232 xoom -portrait
1024 x 768 ipad -landscape
1280 x 752 xoom -landscape
1366 x 768 surface -landscape