We have a lab/collie cross, he was 2 on Monday and has been coming running with me for hte last 6 months. We go three times a week for 6km a time. However I have not run for 17 years so I've had to build up slowley so the dog has too. He manages fine and is always keen to go, the run is 2/3rds off road adn a 1/3rd on road – he like the offroad most as he's off the lead and the ground is soft. We meet up with a few other dogs in the park in the morning so he also gets a good 40 minutes interval training chasing a football everyday too!!
The breed seems spot on for us, softness of a lab (we have a 5 month old son who he is great with) and intelligence(trainability) of a collie. He's very soft and will do pretty much what I say and stay with me anywhere.
He's been biking with me round the woods (2miles) a few times when he was younger and he loved it. He's also been round sherwood pines with us and loved chasing us down the 'downhill' bits. My brother has his sister and she is very similar in nature, we took the two of them round ticknall woods and they loved that too. I would not take him to the peaks or the like as the route would be too much for him and too rocky for him to run over at speed. Don't think I'd like to risk it taking him for anything over 10miles too often though.