I herniated my L5-S1 disc two weeks ago. That disc has given me trouble off and on for years and the volume of yard work this spring did it in. The house we bought last year was greatly neglected, when I say "yard work" I mostly mean "clearing the land". While the acute pain has (mostly) receded, my left leg and foot have significant numbness, likely due to the disc impinging the sciatic nerve. I attempted a very short (~1 mile) test ride on my 'bent the other day and called it quits. It didn't hurt but with the left leg putting out about 50% of its usual strength the right was overworked and that knee started aching.
So...an MRI is being scheduled and I've asked my MD for a referral to a sports medicine specialist. With lower back injuries the MDs seem to declare victory if the patient can do office work and watch American Idol without pain. My fitness goals are rather more ambitious than that, although I can accept that I will probably not be doing the heavy deadlifting/squats I did until about 8 years ago. I shouldn't have stopped - back then my back felt great!
Anyway, the cycling is out for now so I will work on getting some gentle swimming in while continuing with the docs. I had high hopes for good mileage in 2010.