I think that you can make training a lot more fun and improve the speed and accuracy of your obedience.
Granted, dogs do check out, and no one can be attentive all the time, but what you said about the training could be a cause of what you are seeing.
Why Does my Dog Ignore my Commands?
took me forever but I found it!
So checking some clicker training out on the Karen Pryor site, some relationship based training stuff from Suzanne Clothier's site, if you like competing (or not) Denise Fenzi has a nice blog, Dr. Yin's stuff: http://drsophiayin.com/resources/dog_behavior/
checking out calming signals (going slow is one of them) Calming Signals Community
just bits at a time to get back on track with your dog as a fun, fair leader. Thankfully they forgive us!