I was thinking of cycling the 10 km to work and back daily.
Am I going to ruin myself for speed, or is this not that serious? I’d really like to cut back on the driving, and if this could be some kind of general fitness, then great.
If anybody could comment, it would be greatly appreciated.
I think it will help your fitness. I used to ride BMX as a kid (which is similiar to sprinting energy wise) and run 4x per week no problems. I wound up running 11.6 first year in HS. It was XC running that did me in. Maybe you can do intervals on the way home 
I wanted to try the bike tempo video and see how can I fit that into the fall. I still like to mountain bike so I was thinking of using some stuff from the video. Maybe take a big climb and do pushups at the top of a climb!!!
I think it depends on your level, and how hard you ride. The faster a sprinter you are, I think the more negative an impact it can have, and the harder you ride, the more negative an impact it can have. For most sprinters, I don’t think it would be a problem, providing you aren’t stomping hard at a steady-state for 20minutes.
Good stuff. I’m a hacker, so it shoudn’t hurt me too much!