Building a base

I am highly competitive and want to be the best cyclist I can be. I am coming off 2 years of injury, where there was scant cycling or any other exercise. I am looking to eventually get to 20-25 (or more) hours/week for a training base, and I just completed my first 5 hour week in over 2 years. My problem is that I seem to get injured every time I increase mileage, but I have had good luck so far, since I started in March '09.

Friel's book doesn't cover this situation, nor can I locate anyone else who can help me. Obviously, I want to increase my volume as quickly as possible, but safely. I am 27 years old. Anyone have any advice?

Sure, I'll take a stab at your issue.

Well, with your track record of getting injured every time you increase mileage, I suggest you alter your definition of "base". Instead of increased hours, I suggest you gradually increase the intensity of your 5hrs/week from your current
(? don't know for sure as you didn't indicate the intensity) endurance pace to near threshold (after proper warm-up).

From what you state about past injury prone-ness, I don't see 20-25hr/wks in your future. Maybe you can get 10hrs/wk without injury, but 20+ seems to be a stretch, unless you've got your past issues totally resolved...my $0.02CAN worth...

Star low go slow!. The biggest mistake when coming back for any injury is to try to get back to your previous level of training quickly.
Before you begin increasing intensity I would suggest you increase time in the saddle at an easy pace.
Increase you time by no more than 10% per week. You need to give your body time to adapt to the increased work.
If you do the math starting with 5 hrs weekly in 8 weeks you will be riding 10 hrs weekly and 16 weeks more that 20 hrs weekly-
That may seem like a lot of time but you have been inactive for 2 years. Once you reach 20 hrs weekly you should be flying and more importantly injury.

Most overuse injuries occur from increasing either to volume or intensity too quickly and not allowing the body time to adapt. Many cyclists compound the problem by increasing both the volume and intensity at the same time.

Been there, done that!

What was the cause of the injury? If you haven't eliminated the cause of the injury in the first place, then it is likely that it'll come back as soon as you get the right stimulus.

Me for example: I'm 26 and on my 3rd year as a cyclist. During my first two years of riding, around August I needed to take 2 months off to let my knees heal. Both years I was around 1,500 miles on the year when it flared up whenever I tried to increase my volume, no matter how slow I did it. Year number 2, when I went to see a doctor about the pain, he couldn't find anything wrong and called it tendinitis, overuse injury and just told me to give it time. It was just easier for him to label it overuse than dig to find the problem. A good, cycling specific exercise physiologist would have pinpointed the cause of the problem immediately.

This year, I installed wedges on both my shoes, which corrected the biomechanical missalignment and I've been going strong with almost no knee problems at all, and I'm at 7,500 miles for the year riding between 14 and 18 hours a week.

You answered your own question. Stay at ~5hrs a week for a while. You can't expect to be off the bike for so long and jump right back in.

You have to start somewhere and if that somewhere is 5hrs a week then that's better than what you were doing and certainly better than being back on the couch 'cause you're injured.