Tim passed along this article on the similarities and differences of civilian competition vs. combat shooting. The author talks about how the two compare in terms of stress reaction, realities of context, and gear.
Tim commented on the article and offered another article with a different perspective. Both give you something to think about.
The take-away for me is you have to know what your reasons and goals are for shooting. Is it competition? is it self-defense? is it part of your job (e.g. military, police)? What are your reasons? All shooting has stuff in common and so most any sort of education and training will help you out (e.g. a novice needs fundamentals of trigger control, trigger control being critical to getting accurate, acceptable hits, which matter no matter your goal/context). But as you get further along you need to train more specific to your context. Non-specific training can be useful (e.g. shooting IPSC still gives you trigger time), but you have to keep it in perspective and ensure you’re still getting specific training.
Funny… I’m reading Practical Programming by Mark Rippetoe right now and the parallels to this discussion are interesting.
Stuff From Hsoi 
My argument is not that competitions are a substitution for good training but instead something to go along with it. I have found my personal skills improve quickly by shooting competitions.
In some ways competition does augment self-defense training, but mostly I just do it because it’s fun. I realized a while ago that I had probably got all the improvement in my self-defense skills I was going to get out of competition and no longer even try to replicate my carry setup because it just makes me less competitive.