i walk everyday from redfern to the vet buildings (furthest possible from redfern while still on main campus,) and it takes about 25 mins each way. I like the walk in the morning, cos its mostly downhill, but in the arvo it sucks cos its uphill and its usually hot, and i'm usually tired / hungry / just want to get home.
I have tried the walk to central, it takes a bit longer for me, and its not nice since you have to walk right on the side of paramatta rd, which is smelly and noisy and just gross when its raining. And like someone said, you have to walk past about 50 fast food shops which is not the best when you're on your way home and are hungry, but not wanting to get fat....
The refern walk is nicer, you can avoid most of the main roads, and dont have to wait for traffic lights, and once you know your way around, you learn all the side-routes to avoid the crowds (especially useful when its raining and everyone has umbrellas and are being slow)
Also, pedestrians always have right of way on campus (as they are not public roads, normal rules dont apply) and there are lots of pedestrian crossings etc, not like in the city where you have to wait for lights.
Anyway, that my 20 cents worth... go the walk from redfern, you'll be sitting on your bum all day at uni and will prob need the exercise anyway!