Yup, like you guys said. Good practice is the essential thing.
Also, taking a break will help you come back to your guitar refreshed and motivated.
Somedays when I practice, my head keeps wandering elsewhere (especially in the last 2 holyday weeks :p). When that happens, your better off to just put the guitar down and come back to it later.
After all, its supposed to be your pleasure time, not a duty.