First, if you're not familiar with what happened recently in Seattle,watch the video: http://www.bittenandbound.com/2010/06/16/cop-punches-woman-video/.
Let's break it down. Is jaywalking something that should be enforced? Quite simply, yes. If it is a law on the books, then it is enforceable, and should be enforced. If the citizens of Seattle do not want it enforced, then get involved and have it repealed.
Did the officer over react? No. First, although I am not, nor have never been a police officer, I do know that it is standard procedure in most jurisdictions...and common sense to boot that when citing, or simply questioning someone and others insert themselves into the situation, the officer, most especially when alone, must contain the situation. This will often result in at least one individual being handcuffed. The fact that the jaywalker's friend assaulted the officer (pushing is assaulting), thus inserting herself and escalating the situation, the officer was fully within his rights and responsibility to strike her in an effort to gain compliance.
The fact that Seattle has chosen to step up enforcement of jaywalking, again is an issue that will take community involvement to change. From what I know of Seattle, it is known as a pedestrian-friendly city. It only stands to reason that as a matter of public safety, pedestrians choosing to cross traffic lanes outside of marked crosswalks should be cited.