I have a Groovy API, four static methods on a class for accessing LDAP.
According to your mission, you do not want to abstract LDAP, that the end result should be similar to the C libraries with a Groovy feel.
I have a couple of observations:
1) Grails is THE Groovy application and any successful Groovy library should be able to be packaged as a Grails plugin.
2) Closures are nice, but the real power of Groovy is in its collections, which can be made to look like closures by typing .each
3) So far, Groovy LDAP supports basic authentication, a pluggable authentication would be nice
4) Groovy LDAP doesn't have a caching mechanism, these are easy to implement and would also make a nice addition
Finally, I think the mission may be somewhat flawed, JNDI already does this and the reason there is interest in an alternative is because people, at least, I, want to have an abstraction from LDAP. Writing JNDI or even Spring LDAP is tedious, error-prone and time-consuming. A library that doesn't at least attempt to abstract those three things away is not going to get my interest.
I am interested in your project, and I tried to be constructive. I do have some experience with Groovy and LDAP, the yagll (yet another Groovy-LDAP library) open source project on codehaus.org is mine and I have worked with Spring LDAP, gldapo, JNDI and absolutely love Apache Directory Studio.
I wish you luck.