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.
Zaarly is new to me, but yes it seems similar. Probably the biggest difference between the two is that GigYard's service providers are individual people, not businesses.
I'm thinking that sharing it with existing communities that already engage in this way will be the easiest sell. My first target is my neighborhoods Facebook page that has something like 300+ user. Besides that there are a ton of folks attempting to do this type of work with Craigslist's service postings and I'm hoping a few considerate posts there might help.