It really depends on the support you get and give.
As a grad student, I can easily divorce myself from teaching duties and focus on my professional ones. Also, I've had educational pedagogy and theoretical training before hitting the classroom, so I know how to handle myself appropriately. My graduate and coordination faculty are VERY supportive of my efforts and their advice is insightful. Also, being a pharmacist, I can walk away from this job, so I don't get stuck with the really bad duties.
The residents try to be bright and cheerful, but it's quite obvious that they are really tired. The residents only have this duty tacked onto their other clinic duties.
We all try to do a good job, but there just isn't the time for a resident to concentrate on teaching. It is ironic that residents aren't trained in the theoretical (or to a large extent, practical) issues of education, whether it be student or patient.
I enjoy and bring pleasure to my teaching aspect of the career, and I know my students would agree if asked. I can't say the same for the residents...
My own two cents about teaching in a residency:
1. Make sure that it's really training instead of dumping a duty upon you.
2. Make sure you "staffing" requirement is waived during this period (because you are still "staffing")
3. Make it a point to be wild and experimental while grounding yourself in the theoretics. Too many of our practice faculty throw around "critical thinking" without doing it themselves, much less pass it onto their students. Failing to do a good job at this stage isn't a cause for concern if you can rectify it in future experiences.
There's another thread on this subject somewhere as well...