Running every day?
I'm by no means an expert, but from what I've read it's a good idea not to run more than two days in a row and not to leave a gap of more than two days in between runs if you can help it. So going out two days running would probably be fine as long as you don't then go out again the next day! You might find that you get worn out more easily on the second day though, as you won't have had so much time to recover from the first run.
That's a really good question, I think. You need the rest days for your muscles to re-build, especially when you first start. It's worth remembering that exercise doesn't build muscle, rest after exercise does. So it's really important.
That said, as long as a routine has rest built in, it doesn't really matter where. Most training programs beyond c25k have 5 runs a week, some more. You can't have a day off inbetween them all! I regulary trained Tues, Wed, Thurs, Sat, Sun in the build up to a 10k. Worked ok for me.