How often is it ok to board your dogs?

In the last couple of years, mostly between May and October, I've had to frequently travel on weekends (often work related) and cannot bring my three dogs. So they have been boarded a lot. I almost always board them at their vet's and they seem to do fine. I guess I'm just feeling some guilt or separation anxiety. From May to October it's been an average of two weekends a month, plus about 10 days in July. They really seem happy and well adjusted...maybe I just want to hear that it's ok. Thoughts, comments are most appreciated. Thanks!