I have registered for 3 services of this variety, all three were free for a basic listing which is all I elected to do at this point. One offers a service where customers can basically type up a description of the job and it gets emailed to all of the people who fit their needs but you only get the contact information if you are a paid advertiser with the site so--your contact information is on display so clients do have the option of contacting you directly. With this site in particular it costs quite a bit to advertise with them so unless I find that I am receiving a lot of the emails with leads it probably won't be worth it for me. So far I have not had any calls as a result of registering with these sites but it has only been a few weeks.
I also registered with a major map/search engine so I in theory show up on a map search for professional organizers within my area but since I am a new company I apparently need to make my web presence a little bigger before that will happen (it does show up if you search directly for my company's name though.)