YES, pool running is great if you are hurt. Kevin Sullivan (Canadian Olympic Miler) is proof that you can come out of the pool and make the Olympic team a matter of weeks later if you stick to a good plan (keep in mind he was already in great shape going into the pool). A good read (with better reads through the links on the page) can be found here: http://sweatscience.com/the-physiology-of-aquafit-and-pool-running/
Linking to this page: http://www.theglobeandmail.com/life/health/alex-hutchinson/the-future-of-fitness-may-be-in-the-pool/article1930179/
Shows the workout he used at the time. To summarize for those who don't want to read the entire article the workout is as follows:
HARD/EASY
5 minutes/2.5 minutes
4 minutes/2 minutes (times 2)
3 minutes/1.5 minutes (times 3)
2 minutes/1 minute (times 4)
1 minute/30 seconds (times 5)
30 seconds/15 seconds (times 6)
15 seconds/10 seconds (times 7)
I actually used to use that workout when I was hurt for a 2-month period once. My ramp-up time to running strong was much shorter than previous injury periods where I spent no time in the pool doing aqua-jogging. Just remember, it is hard to gauge effort so you are your own gauge of how hard you want to go. If you think you are maxed out, go harder. However, if you are in pain with the aqua-jogging, it might not be a good idea to pursue this. Still, routine aqua-jogging can be a good replacement workout if you are hurt. I would reco you do hard workouts according the schedule you would normally do your hard running workouts on land. For example, if you run hard 3 times a week I'd do pool-sprinting 3 times a week.