I'm currently working for PwC and we are constantly getting emails about them raising the "finders" bonus for outside hiring. I don't know about the other big 4 but ever since the recession and the fact that they cut down hiring and people are leaving, we are now desperate for people! I would recommend applying ASAP. I'm in the Pittsburgh office but I know that from talking with our PwC people all offices are looking to hire external or from anywhere for that matter.
PWC is definitely increasing hiring across the board in all groups, more than the rest of the firms. But the other firms have also begun to advertise referral awards since the need for personnel in 1-2 groups have increased. Linkedin may be a good resource to find recruiter contacts for those interested.