The training agencies have been very helpful in producing special tables with the new no-stop limits, based on the mix you are using. So you can stay on your favourite wreck quite a bit longer. The course will cost a lot, is mostly maths and I won't even go diving. For such benefits as increased no-stop times and safety, I think that is good value for money. And prices are falling.
Nitrox courses are fairly simple.
We are not talking rocket science here. Besides, a lot of us, instructors included, get lazy about table use and could do with a refresher. There are no skills to learn, no drills, nothing but enjoying your dive and the planning element. So you can learn it all in a classroom, but resort courses are becoming more popular. On a boat or on land in some exotic destination, learning and diving nitrox is possible all in one day.