I use REST web services to manage the users accounts but database enrolment to enrol students into courses. Currently as far as I know, the built in web services for Moodle 2.0.1 does not expose access to course contextid or the roleid which you would need to enrol a user on a course through webservices. Access to contextids is in the roadmap but when that will be released I do not know.
Database enrolment has a problem at the moment as it will only set the role of the user to the default value in the configuration, it ignores what is in the database. However this has been reported to be fixed in release 2.0.2