What really helps me keep burn-out at bay is ds' consistent early bedtime (8pm). From 8pm on, I do nothing except watch TV, read, knit, etc. It is my re-charge time.
Additionally, I try to make sure I give myself some 'me' time before I reach my burn-out level but sometimes I overestimate my endurance level or I wil just have a lot going on and get too busy and preoccupied.
So, when I do reach burn-out, I will try call in a babysitter, neighbor, colleague, etc to stay with ds for a couple of hours, so I can just be alone (go to the bookstore, sit on the beach, etc.).
If I cannot find someone, I curl up on the couch with ds, put in a "long movie" and just sleep while he watches his movie.
Sometimes, I just pile him in the car, give him my iPod to listen to his books on tape and drive for awhile.
And, I have also been known to take him to the gym childcare center (which he loves, as they have a giant bouncer) and just lounge on the couch in the locker room reading a book for 2 hours.
It is hard.