I have been there done that, twice! Key to recovery is allowing the bone time to heal without over stressing the bone in the healing process. Do not do any heavy lifting or mountain biking until you are well healed. Most broken collar bones heal in about 6 to 8 weeks. To keep your lower extremity fitness up, ride a recumbent trainer or if you can find someone with a recumbent trike, you can get some easy road miles in. Do gentle exercises with your involved arm. Lean over at the waist of the affected side and let your arm dangle like a pendulum and working in clockwise and counter clockwise circles to keep the shoulder joint limber. Your collar bone will let you know when you can gradually increase your range of motion, gradually bringing your arm up to 90 degrees at the shoulder then eventually overhead. The clue of progress will be your diminshing pain with movement. Now if you are a well paid pro, you can even win a race on l'Alp d'Huez with a broken collarbone
http://news.bbc.co.uk/sport1/hi/othe...03/3090517.stm , but I recommend going easy for the next 8 weeks.