Thanks for the recommendations. I think I have been neglecting mobility work and soft tissue work.
I think this may have been exactly what I needed to hear. I just took off my shoes and socks and tried it out and it felt much more stable. I'm not sure if my gym will let me lift barefoot but I think I can get around that by bringing my yoga mat with me. People already look at me like I'm crazy at my gym, now I'll be the weirdo that uses a yoga mat for weightlifting. I am definitely going to look into getting a pair of the Nike Frees. Thanks!
I'm only doing them once a week and I've got only one session with them left on the program I'm on right now. After a short break (2 week trip to Germany) I'm planning on starting the WSFSB3 template and I'd like to keep working on this exercise so I'll see where it can fit in there. I really enjoy the challenge of the various single-leg exercises.
My concentration is usually great but last time with these balance issues causing frustration I wasn't as focused as usual--I'm sure that was adding to my problems.
It sounds like barefoot is the way to go. Thanks.
Thanks again, everyone. These answers were really helpful. I love T-Nation! (And I have boundless newbie enthusiasm, ha!)