I feel like I should really jump here in to support much of what rhyme has said. My background: 3rd-year strategy consultant.
Hours
Consultants in my office average 55-60 hours per week (including travel, but excluding breaks). We track these numbers and post them in our breakroom. Since I'm a nerd, I keep track of my hours and can tell you that over the past 2 1/2 years I have averaged 57 hours, with a range of 40-93 hours in a week.
Another note on fixed price vs. T&E contracts. Most of my firm's engagements are fixed, so I don't know how T&E feels. But consider this: if the project is T&E, then the firm is probably going to want you to work as many hours as possible - it's charged to the client and drives revenue, after all. So I'm not sure that fixed is any worse than T&E.
Social Life
I think many firms attempt to support some kind of work/life balance. At the end of the day, our people are our product and we try to keep attrition low. Part of that requires allowing people to have sustainable family and social lives. I will note, however, that the first-year consultants (post-undergrad and post-MBA) don't have the best social lives as they're trying to "prove themselves."
In general, weekends are dedicated family time. However, if you are working from your home office (which likely means you are on a pure strategy case) then nights after ~7-8PM are up for grabs too. Typically, I will work until 6 or 7 and then go home, cook dinner with my roommate, and then work for a couple hours after dinner. I should also note that, over the past month, I have gone to a concert and two hockey games during the week - and they were all company tickets.
One last note: some of my co-workers have terrible social lives and they also have terrible hours. They're not any less competent, nor do they have the worst projects. The common thread among all of them is that they fail to set boundaries and they allow their partners/managers to stomp all over them.
Travel
Some firms make you travel 4-5 days a week. Right now, I am traveling 3-4 days a week (fly out Monday morning, return Thursday evening). Fridays are pretty much mandatory "home office" days and everybody is expected to be participating in various office activities and responsibilities.
Again, my strategy work kept me seated in my home office almost 5 days a week. In fact, only 2 of my 7 projects have been weekly travel projects. I would travel ~once a month to make presentations to the client, but that's pretty sustainable. Most client interaction would occur over teleconferences. And this makes perfect sense. If you are trying to improve your client's profitability, then why would you add to their cost burden by charging expensive airfare, hotel, rental car and meals if you didn't
really need to? On that note, I never charge business or first class to my client, and I always reserve the cheapest rooms at our preferred hotels (Hyatt/Hilton/Starwood). I'd like to think that my co-workers and I aren't
that high maintenance.
Sleep
I get ~6 hours/night during the week, but not because I'm working late. It's because I surf the internet and post messages on forums like this one.
Seriously, I think consulting is just like college in that there are definite "spike" periods. At the beginning of a case, right before major presentations, and at the end, hours go up. All other times are more sustainable. Just like college with midterms and finals.
Quality of the Projects
Can't say much here since it varies so much, but I will say that you need to take charge of your career and position yourself to get on the projects that are best for you. Although my firm uses the "jack of all trades" approach, I can say that I have specialized exclusively in the Aerospace & Defense and Technology industries. Why? Because I'm really interested in these industries, and if I'm really interested in them then I'm going to perform better and pull in a higher bonus. Again, it's just like college: choose a major that you're interested in, because then you'll get better grades and get a better job.
Exit Opportunities
McKinsey gets the best, I think. Most of the consultants who leave my firm tend to go to former clients (and that's not a bad thing at all - they're great clients). We also get contacted fairly frequently by headhunters. I've had a couple opportunities come my way that pay better than my firm. I've stuck around because I love my company.
Side Note on Internal Consultants
Some companies have their own internal consultants, most often affiliated with their strategy department. These consultants go out, assess business units, and develop recommendations to improve profitability. These consultants are good because they understand their business better. These consultants are not as good because they don't have the experience of the consulting firms. But if you would like more stability (including likely better hours and less travel), then I would consider a career as an internal consultant.
Moral of the Story
Not all consulting firms are alike, and consulting does not equal McKinsey & Company. Many of the stories that you hear are from McKinsey, but that's not the only option. Other firms like Monitor, Bain and BCG, and the list goes on, are wonderful options. These are successful firms that make their money by
differentiating themselves from McKinsey. It's the first rule of strategy. And they succeed. Picking the consulting firm that's best for you is like picking a business school: find the place that's the best fit for you, and don't be so damned set on HBS. I'm looking forward to recruiting the next generation of consultants from Kellogg!