I took a group lesson my 2nd time snowboarding (took it up this season) my first time was just an hour on the bunny slope trying to stand up (We arrived late just before closing) etc. so doesn't really count. I found the lesson good for showing the basics, but due to having a very slow learner in the group (it was a group of 3) and very bad teaching conditions (blizzard basically so hard to hear/see instruction) I didn't get much out of it and it kind of put me off lessons, so the next 3 or 4 times I went I just practiced myself and was able to get down greens okay etc. but I knew my technique wasn't great and I was more in survival mood (get down by any means) than getting down in a fast and nice looking fashion. I was still having a blast though. After I kind of hit my wall of how far I could get without further instruction I took 3 more lessons (2 Full day, and 1 Half Day). They were technically group lessons but I never had more than 3 people and had one or two private ones (good odds of not having more than 1 or 2 others or even by yourself on a weekday once you are not in the very beginner lesson) with a great instructor so I learnt a LOT and had a ton of fun.
Now I can go out by myself and have a lot of fun and work on improving but the lessons were essential to me getting to that stage. If nothing else it was good motivation and a good confidence builder and really good fun, you get to see the mountain in a safe way (No wrong turns down blacks, well not too many anyways
) and if you're lucky enough to get a combination of a good instructor, a small group and other people of similar ability it really is the best way to learn how to snowboard.
I guess my advice to you would be to use the lessons to get to a level where you feel comfortable enough to practice on the bunny hill/mild green and assured of the basics of technique. My main stumbling block with snowboarding was not being confident enough in my technique to really go for it on greens/blues, if you take the time to practice and ask the right questions in the lessons you will grow in confidence quickly and really enjoy your time on the slopes.
Oh and ditto on the learning how to fall, my first time out I sprained both my wrists, bruised my tail-bone and ribs and generally came out black and blue. Conditions had a lot to do with this, it was a sheet of ice and I was just messing around by myself, but I can see how a lot of people pack it in after their first time if they get enough bad falls, once I learnt how to minimise the pain by falling properly (at least until I started going a bit faster/trying little jumps etc.) I started to really enjoy it!