It never gave me trouble with Google Chrome. IE doesn't always open a world for me, though. Or if it does, it does it minutes later.
EDIT: After reading the post below, I should add that I don't have any problem as long as I let the page load first. If I try to login before the page finishes loading, even with Chrome (I can type my name and password in about one second, and the advertisements on the logout page sometimes take several seconds to load), I get the "No world is available right now!" message.