It works on all the browsers I tested (latest versions of IE, Firefox, Opera & Safari).
Not really useful, maybe on the off chance that, say, you need httpOnly cookies for some reason, and you can see headers for part of a path (e.g. because there's a phpinfo page in the root, but the cookie is for /app), or whatever, supposedly this was considered a security issue by Secunia way back when you could use %2e%2e/ on all servers in all browsers: http://secunia.com/advisories/9680/ (Though I think the premise for that bug is that you can't jump pages, which is of course wrong)
