I don't keep close tabs of my friends and classmates' money situation, but it seems like everyone is going to be different.
Some have little to no debt. Some took on the max. Most probably took somewhere in between. If you want to calculate payments, use the "PMT" function in Excel. As for signing bonuses, it's all over the place - only really applies to those who went to banking or consulting. If you work for a startup, VC, other fund, nonprofit, marketing, etc. you may get little to none. And those folks don't necessarily get job offers during the school year - but shortly after when school ends (simply because firms outside of the MBA feeders don't give offers 3-6 months in advance; they tend to give the offer and ask "can you start next week?").
Some folks buy a house/condo right away, others don't. Depends on the individual - not on whether they had an MBA or not. Some are married, some come from wealthy families (and don't need to work or can just buy real estate), blah blah blah.
Again, there is no typical situation.
What does change for many folks though isn't really related to MBA -- but has more to do with the stage of life they're in.
First 2 years post-MBA -- lots of weddings, and lots of babies (especially 3-5 years out). If this happens to you, that certainly changes your lifestyle much much more than anything.
As for alumni, it's not as big a deal as you'd think. It's not a secret club. At most alumni events (I've heard this from folks at other top schools as well), the majority who attend tend to be recent grads (0-3 years out), and then trickles off. It's not like these things are attended by crowds of alums who are 10-20 years out (by then, alums in their late 30s - 50s are far more preoccupied with their families, personal life, etc and would much rather spend their free time with that than hobnobbing with a bunch of strangers and "kids" in their 20s and 30s). And people learn very quickly that when you get a bunch of alums together on a social occasion like this, people avoid talking about work - again, it's mostly about personal stuff like family life, hobbies, vacations/travel, etc.
As for fast tracking, it's not really the case. There tends to be a lot of movement in the first 2-3 years (esp in a bad economy) -- people jumping from one firm or industry or region to the next (not necessarily jumping "up" but more lateral moves) -- basically a trial-and-error process of finding the right job situation that best suits your career and family/personal life. Things tend to stabilize (i.e. stay in the same job for a longer time) after 2-3 years. At least that's what I've seen. You don't really truly know what kind of job situation suits you best until you're actually in the thick of it - some folks I knew were very skeptical and wary of their "consulting job' before even starting, but ended up sticking it out for all this time. Others were very gung ho about whatever job it was (consulting,banking, vc, pe, etc) only to leave after a year or two to do something completely different (like have babies, start a business, move to some foreign country, work some other corporate job, etc.)
Treat the money you spend on an MBA as a consumption good, not a true investment. It's money you're spending for the 2-year experience - so make the most of it. The practical benefits of an MBA are really difficult to define (if at all) after 5 years or so - since by then your ability to move up the chain or get access to funding for your biz or whatever will have little to do with your MBA, and more to do with your entire body of work.
It's easy to overestimate the medium- or long-term importance of the MBA as an applicant or student -- because for you guys, it's in the "present tense" - it's what you're experiencing right now, so of course you're going to think it's extremely important (as you should - that way, you will make the most of your experience).