url loading bar blocks access to the top of the screen, making it impossible to interact with, say, facebook notifications until the full page has loaded.
the url bar is dismissable when the page is finished loading, but not before. {note that the url bar stays loading for 2min on facebook}

some ideas:
1) dont differentiate between the loading state and the non-loading state. it the users wishes to wait for the page to load properly before interacting, they can, if not they just tap empty space like normal.
2) indicate loading at the bottom, where the user can scroll/zoom to get at the things underneath
3) move the url bar to the bottom, where it is less likely to interfere
4) make the loading url bar look very different than the url bar, make it a little more transparent, and let the user tap stuff underneath it. {allow interacting with it only after you bring up the overlay.}