Is there any draw backs from to much exercise? I currently start my day with 15 minutes of stretches followed by 25 minutes of Slim in 6 start it up, then through the day I usually play around with the wii fit for half an hour to 45 minutes, and every evening I walk the dog for about 45 minutes, and it is a good brisk walk.

Too much exercise is relative. For some people, a flight of stairs is too much, while some can do 100 mile ultramarathons. If you aren't too exhausted, experiencing sleep deprivation, or injury, and are generally still healthy, then the amount is just fine

I walk the dog 2 hours a day and do 1 hour of weight training...

That sounds like a fine amount.

I hiked for 8 hours on Saturday. Sometimes I bike for 4. Sometimes I do yoga for 1.5.

What I realized was, back when I did nothing, I never once asked myself "am I exercising too little? Is this bad for me?"

Yes there is a drawback (google over training) but I don't think you're doing too much. But like the pp said it's all relative.