Here's what we did:

8 weeks to 6 months:
When we went out, we left Tails in the hallway. It's quite long and in there he had his bed at one end, toys and cushions in the middle and two puppy toilet pads at the other end (we live in an apartment and pad training worked great for us too.. and the progression from pads to outside just happened naturally -ie. as soon as Tails found that he could hold it a bit longer he decided that he just preferred to go outside).

6 months til now (10 months): Now he probably would be fine with the run of the flat when we are out, but just to be safe we shut the living room and my work studio.. so he has the hallway, the kitchen and the bedroom. I know he likes to lie on the bed and we leave toys in the hallway and water/treatball in the kitchen. Lily and I work from home so we're not usually out that much anyway.. if its more than 5 hours we send Tails to the dog man. He would probably be fine for longer than 5 hours but I just think its gotta get boring... after all dogs can't browse the internet or watch TV. We leave audio lectures on the Bible or Rabinic Hebrew playing when we're out.. or sometimes a bit of bluegrass.