It depends on how much $$$ the customer has. I used to travel to Tucson, AZ for regular accounts. Now I just stay with 100 miles from home. I do enjoy the occasional overnight trip though every now and then.
I have gone up to an hour and a half one way. Of course you need to have enough jobs in that area to make it worth it. Another thing that works is if there are small towns along the way that you can pick up accounts in so the trip there or back your making money.