Well...here is my opinion about joining the BL online challenge. If you have a GOOD solid knowledge of what healthy foods are and what kind of exercise you should be doing, you could probably do it on your own.
But if this is your first attempt at a healthy living lifestyle and if you know little about what you actually need to do, then I would suggest joining some sort of program, be it the BL group or WW or something like that.
There are truly people out there who know little/nothing about what healthy eating actually is!! These are the folks who see the "smart choice" labels on things like Froot Loops and think that this is a great choice for breakfast!!

If you are this kind of person, no offense, but you need HELP. But if you have a firm understanding of fruits and veggies, lean proteins, etc, then you could probably do it on your own.
My suggestion would be to start out with a program of some sort. Stick with it for a while and then, if you are doing well, maybe you could consider going it on your own for a while.
I have been doing WW on my own for almost two years now.... but I have joined WW and do the whole weekly meeting thing NUMEROUS times in the past (sometimes with more success, sometimes with less), so I KNEW that I could do this on my own. I have the tools and the knowledge. Plus I have never stopped reading and learning about healthy eating, exercise, etc. I am CONTINUALLY learning new things and tweaking my food and exercise plans. But I'm not sure I could have continued on my own for this long if I didn't have all of my friends here on the WISH board. Having a place to come and be encouraged and to encourage others has been a SAVIOR for me.
Good luck with whatever you decide to do.................P