My girlfriend was also pretty impressed with the documentary. She's already made the decision that she wants to go to naturist places and events with me but I think the film did help to show her that young naturists are no different to young textiles, except in attitudes to nudity.
Some specific thoughts:
Much has already been said on Channel 4's choice of title (obviously they were going for the "lonely masturbator" demographic...) as it really didn't fit the film that well. But Mollie did seem to be the core of the film.
Mollie came across as probably more typical of youth generally than of youth naturism. There's lots of young women who see nothing wrong with topless sunbathing and skinny-dipping; these aren't activities exclusive to naturism. She seemed to mostly draw the line at full nudity but maybe that was down to her choosing to disrobe in pretty public places in the company of people who weren't willing to be naked. She came across well with her body-positive attitude but I don't think she was actually as unique as the film maybe wanted her to be.
Alex topless in Manchester highlighted as usual that there are some problems governing the enforcement of public nudity laws in this country - while it is not illegal to be naked in public, you can be arrested by police who seem to be unaware of exactly what is acceptable and so feel that they should err on the side of caution and let the courts worry about what behaviour is and isn't allowed under law.
The person who said that promoting body-positivity was easier for those with conventionally-attractive bodies had a point but someone having a "good" body should be no barrier to criticising the notion that there are "good" and "bad" bodies in the first place. Sure, it might be more encouraging to others so see people of all shapes and sizes being confident naked but anyone being confident naked (even if society tells them they should have no reason not to be) is a positive step.
Something that was emphasised less in the film was interaction between the older generation of naturists and the younger one. We were told that BN were desperate to recruit new members (which was where Daryl came in and did his job well) but the real test for encouraging young people to get involved in the more traditional aspects of naturism (social events, clubs and spas rather than skinny-dipping on holiday and riding in the WNBR) is in ensuring that when they come into those situations for the first time they don't encounter an "old person's world" with nothing offered to encourage them to stay involved beyond the opportunity to be naked without worry.
So it would have been nice (and potentially more encouraging to young people interested in naturism) to see more of YBN and the activities they put on, rather than just focussing on the recruitment of new members (although the Bristol university society Jesse has started is impressive, especially given that most universities require around 6-10 interested people before they will grant a society official status - so by the time of the fresher's fair shown in the film, they must already have managed to drum up some significant interest by themselves!)