TaskRabbit seems to focus more on simple errands that anybody can do and handles the details for you. They describe it as "Your to-do's, done".
GigYard focuses on helping people describe their unique qualifications so that they can be offered as specific services. Then gives customers the tools sort through those qualifications in order to find what they're looking for. It also takes a more hands off approach and expects that the customer and service provider work together. Similar to the way Craigslist works for buyers and sellers.