Weekends are forced vacation too. It'd be great if companies adopted a "floating weekends" policy too, for the same reasons I outlined, but no company I've come across seems to do so, officially (you do see unofficially here and there bosses who recognize an employee working the weekend and allow them to take a couple days off later, and simply not reporting the vacation).

As to your first question, yes I've experienced both. Not month long shutdowns, but week long ones, but it's the same thing: if it's not convenient for you to take a vacation during that time, it's pretty much a waste and it sucks. If your spouse doesn't get 4 weeks off on August, are you going to go on a 4 week vacation then? Probably not. But then you'll resent the people who do actually take that 4 weeks off to go somewhere. It's bad for morale.

I agree that a solid 4 week vacation is enriching, but just declaring an arbitrary 4 week shutdown is a cop out. Fix the structural problems that require every one to be in the office at once, and then give everyone that much vacation time to be used when they like it. I'm not saying that this is easy to fix, but if you really believe in giving people time to have significantly different experiences in their lives, this is what you'd have to work at.