I've been doing CrossFit for 2 years. And... I love it.
Some general advice on starting CrossFit:
Start slowly. 2 times per week might be plenty, as months pass try making it 3, 4 and eventually 5 times per week (if that's what you want of course, but never do more then 5 on the long term). Also, every 4 weeks take it easy for a week so your body can recover for a bit. Every 8 weeks take a whole week of no (or very little) exercise.
As for the workouts, try familiarizing yourself with the techniques before trying to do prescribed weights. Don't cheat with crappy technique, because in the end you can only cheat yourself with it (and you'll hurt yourself as you get to higher weights). Be careful with new techniques that are hard to master, take it easy: it takes time and training. Everything does :)
I'm training at a CrossFit-gym, so I don't do any of the programming myself. But from what I know, programming is very important to keep your body developing and, not less important, keep you from getting bored. Repetition is a killer. Keep workouts varied (as all CrossFit-sites say). This is pretty hard, because you can't randomly trow workouts at yourself: you need a long-term plan. Follow the main-site or a proper CrossFit-gym and follow their Workouts if you haven't got access to a gym yourself.
You should be aware that CrossFit will get you fit, but you won't (most probably) win the Olympic Games with them. The whole idea of CrossFit is not to specialize (it's for insects :p). Also the goal is not visual muscle-gain, you should start bodybuilding if you want that. But if you want to get fit, possibly as fit in the broadest sense as you can be, CrossFit is the thing to do.
To get to the point: I think most people who 'hate' CrossFit do so because they get themselves injured or over-trained by bad programming, overestimating themselves, recklessness and bad technique, getting bored by bad, repetitive programming or expect to reach things CrossFit is not at all about.
Good luck with choosing what's right for you. CrossFit isn't for everyone, but it is for people who want to get fit, learn and do things they didn't thought possible and basically enjoy working out. Once you get into it, you'll realize there is so much to learn (snatches, butterfly kips, handstand walking, flags and other crazy stuff) and there are so many things to improve, that it'll blow your mind. At least that's what it did to mine ;)
And to answer your last question:
I didn't supplement the training (I train 5 times per week now and on top of that 1 day of technique-training), but for my 5-month hiking trip I did train for hiking specifically. Again: CrossFit isn't specialized, so if you do wanna do something specific: train for it specifically and specialize ;)