A few thoughts.
First, I certainly don't mean to disparage any summer associates, but the vast, vast majority of summers have no idea what life as an actual associate is like. Summer associates routinely are coddled, given "interesting work" and rarely ever see an unreasonable deadline. Just as summer associates are interviewing for a full time position, the law firm is interviewing to make sure the summer associate likes the firm and has good things to say to their fellow classmates and career service offices. Certainly summer associates get to see what is going on around them, but from my experience it is a completely different world. Associates (and partners) are on the whole very cognizant of what summer associates see and the type of work they get to work on and almost uniformly don't want summer associate to be overworked.
Additionally, it is far easier to work long hours (something that the vast majority of summers don't actually do for more than a few days, if ever) when you know you have "summer events" and nice lunches and dinners sprinkled throughout the summer. That probably colors summer associates' viewpoints more than anything else. That and the fact that it is new and exciting.
Second, on to the question at hand. As another commented noted, this is entirely practice group dependent. Even at a firm "known to be a sweatshop" not all associate experiences are equal. Certain practices - the service groups generally - have better QoL because typically deal timelines are not as compressed. For example, on a capital markets transaction, if there is a real estate component to the deal, then the real estate department is usually (but not always) informed early on in the process and they are given more leeway to complete the task at hand. The deal documents can be freely exchanged by the main capital markets team with the caveat that all real estate issues are subject to comments from the real estate group. In that regard, no one is typically waiting around for these comments like they would if they were a deal document from the main practice group itself. While the real estate group isn't given weeks to do rather simple tasks, a few days extra often means working over the weekend an doing that same work on a Monday.
However, not all service groups are created equal. Some service groups may in fact push their associates quite hard, while the same group at a different firm may not. You won't really get a feel until you actually see the group.
Third, more telling than aggregate billed hours is the ability to plan when you actually bill those hours. Most associates have worked hard and have put in long hours previously (we almost all do pass the bar in fact) and will put in long hours as an associate. The real issue in my opinion is the ability to actually plan your life around the long hours you put in. Some firms are very flexible about working remotely on the weekends (and even occasionally during the work week). Other firms that is not the protocol and all work is generally done at the office. The only way to really get an understanding of this is to show up at the office on the weekend to see who is there and who isn't there. I would encourage all summer associates to do this at least a few times over the summer. It can be as simple as saying you stopped by the office because you left your jacket there or some other excuse.
Likewise, some groups expect work to be done immediately when assigned, even if on Friday night. Sometimes, this is required. But often, there is a culture that work is to be completed immediately, even over the weekend, when in fact the work doesn't need to be completed immediately but must be done prior to the beginning of work on Monday (this is part of the perk of working in a service group).