It's not that people gain back all the weight and more when they eat carbs again (actually, we never stop eating carbs...we just change how many and where they come from), it's that they go back to the way that they were eating before that got them overweight in the first place and that will happen no matter HOW you lost the weight.
I think the only people that have a hard time eating like this forever are those that go into it with a "diet" mentality, ie "this is something that I'm going to do until I lose the pounds and then it's back to business as usual". This has to be a permanent change in eating habits or the weight won't stay off.
As for how hard it is? Well...there's lots of people here who have been living low carb for 5 years or more and Dr. Atkins did it for a lot longer than that. Yes, it's quite do-able with the right mentality.