The last time it was measured, I believe in 1999 after a major knee injury to the same leg, it was right around 1 1/4 inch. I do remember having that option of going in and pinning the normal leg for it not to grow (soon after the fracture). I can't be sure of the reasons why I chose not to, but if Daniel's discrepancy has a chance to get larger, it sounds like a good idea to me (although I am not a doctor). Not sure what "IIRC" is but I can tell you that 1 1/4 inch is noticeable in every day life.
I do have heel lifts in a couple pair of shoes like Johnnys Zoo has mentioned, and in the past have had shoes built up. Mostly only on tennis or sports shoes. The 3/4 inch heel lift is the largest I found that will fit reasonably in limited shoes. The built up shoes I have had never really worked for me, but I'm sure the technology is better now.
"Can you tell how much total difference you had?", yes I can. If I'm at the beach or walk for longer distances with my child in flip flops, you bet I feel it in my back and more my knee, but thats a whole different story. For example, if I walk 18 holes of golf, the limp form the length discrepancy dose get to me and my back, but I would not consider myself to have a bad back, just a little tight. I have two orthopedic doctors in my family and they are both really worried about my back long term, and they are strongly urging a leg lengthening procedure. It is their opinion that the shoe fix is not sufficient, in addition to the doctor that put my knees back together over the years.
But overall I do believe the back could be a major issue in the future. As of now, there is nothing my leg length discrepancy stops me from doing. I am limited more from multiple knee injuries. I play hockey once a week in a mens league (hockey skates are lifted on one skate), biking is fine, golf is fine, although sore after walking. I just don't run...that is the worst both on my back and knee. It made training a bit more difficult, I had to substitute lots of bike for the track workouts the team had us do.
Not sure I have answered anything, but I hope it helps. Keep me posted on Daniel's progress. Sounds like regardless there will be a 1 1/4 inch difference. Everyday life not a big deal, in sports and/or skiing it could be really different. The lift on my boot was essential for my ski career, would not have been possible otherwise, I'm sure of that.