Perhaps my most favorite thing about OBO is that it is not based off IE, and it's not dependent on it either. But anyway, here are some pros, and cons.
-1.2mb standalone portable file
-has tabbed browsing
-has basic features (back, forward, home, refresh, favorites, print, open file, save, Find, zoom text/font, history, cookies, etc)
-a ton of options to disable or enable (such as "load images", "enable image animaton," "save forward history," etc)
-no url bar (have to click "Navigate to URL", or Ctrl+W)
-U-u-u-u-UGLY! Very poor graphics....
HTML is fully supported, but that doesn't mean it always looks pretty. More advanced pages (like Facebook) look like mobile web sites on your phone. But it works, and that's what counts.