I've developed an additional service to implement Drupal content searching. This service provides one method, search.searchData, which uses Drupal's hook_search (and is closely based on the Drupal API command search_data).
The service accepts up to three arguments:
- search_keys: the keywords for the search
- type (optional): the type of data to search (i.e. 'node', 'user')
- simple (optional): if set, the search returns only the main fields (link, type, title, user, date, snippet) and removes any additional data
You can see a demonstration of this on my site at:
http://arithmetric.com
I'd like to see this eventually included with the Services module. For now, I've packaged it as a stand-alone add-on for Services. You can download it from:
http://arithmetric.com/files/search_service-20080207.tar.gz
Install it by uncompressing the archive in your modules/services/services directory (the location of node_service, user_service, etc.) and enabling the Search Service module.

Comments
Awesome!
Great work! Would you mind creating an issue on it in the Services issue queue? This is definitely something that should go into the Services module.
Created issue
Thanks Rob. I've added an issue here:
http://drupal.org/node/219399