Second vote for searchmaster's response as the only legit one yet.
I am an IP attorney. Within my specialty there are two sub-specialties - client counseling/prosecution, and litigation (enforcement). They require vastly different skill sets. Both types need to be able to write effectively and persuasively. Litigators have a little easier job in that regard, in that their writings are for a more limited audience. I.e., they typically write for a judge or jury. In contrast, patent prosecutors write patent applications for three different audiences - the public, a USPTO examiner, and the court. Both must also know and understand the law, though prosecutors generally need to know a little less of it than litigators.
Apart from being able to write and knowledge of the law, patent prosecutors must be smart and possess a highly flexible mind. I've been working in the field for 15+ years and I have never written a case that was "right up my alley" from a technical standpoint. I live and die by my ability to quickly understand and assess new technology, and my ability to have cogent conversations with inventors and clients. Any patent prosecution attorney who lacks those skills will be significantly limited in the type of technology they can work on, and therefore only good in large law firms who have a large client base in that area. Patent prosecution attorneys also have to have the ability to perceive and understand potential future problems and address them in the documents they prepare.
In contrast to prosecutors, patent litigators are primarily detectives and look backwards at cases for any problems/issues that help their client's case. Thus, critical skills for patent litigators include knowledge of the law, persuasive writing, and extreme attention to detail. An excellent work ethic and the ability to work in a team based environment also helps a lot.
As for attorneys in general, if I had to pinpoint one necessary skill that delimits good attorneys from bad, its the ability to listen and understand what a potential client wants. You would not beleive how many attorneys lack that basic skill.