Our lab doesn't much go outside in the day, she will go out and hair round like an idiot for about 20 minutes (nicknamed "The-wolf-half-hour") but other then that, she is happy inside wandering round where ever we go. If you get up and leave the room, you expect her to be there, if you turn round and she is not there, you find yourself wondering if she's ok. However, she has the option of asking to go out when ever she wants.
I wouldn't personally be happy leaving her all day on her own, I remember watching a time lapse film of a big dog in the house on his own on TV once, and he spent all his time between the sofa and getting up to go look out of the window to see if anyone was coming home yet. I expect it was an emotive film because the set the sound of a ticking grandfather clock over the video, so you really got an idea of time passing for him. It just doesn't seem right to put a big, social, animal in a solitary situation all day. I would expect some destruction/boredom issues if this is a young animal, but an older one would probably be lonely, though he wouldn't destroy your house.
It's one of those things like the last thread I was reading about flaming and the whole "if you do that, this will happen" argument. Some people do it and it's ok for them, some people don't think it's right to do so it doesn't work for them. Maybe two would be better company for each other? maybe two would be twice the problem?
We only got Sasha because Dan is home all day and he wanted a companion too. They make a good pair.